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Title: A Monograph on the Sub-class Cirripedia (Volume 1 of 2)

The Lepadidae; or, Pedunculated Cirripedes

Author: Charles Darwin

Release Date: March 8, 2010 [EBook #31558]

Language: English

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List of Species

Lepas

67

1. Lepas anatifera

73

2. Lepas Hillii

77

3. Lepas anserifera

81

4. Lepas pectinata

86

5. Lepas australis

89

6. Lepas fascicularis

92

Pæcilasma

99

1. Pæcilasma Kæmpferi

102

2. Pæcilasma aurantia

105

3. Pæcilasma crassa

107

4. Pæcilasma fissa

109

5. Pæcilasma eburnea

112

Dichelaspis

115

1. Dichelaspis Warwickii

120

2. Dichelaspis Grayii

123

3. Dichelaspis pellucida

125

4. Dichelaspis Lowei

128

5. Dichelaspis orthogonia

130

Oxynaspis

133

1. Oxynaspis celata

134

Conchoderma

136

1. Conchoderma aurita

141

2. Conchoderma virgata

146

C. virgata, var. chelonophilus

151

C. virgata, var. Olfersii

152

3. Conchoderma Hunteri

153

Alepas

156

1. Alepas minuta

160

2. Alepas parasita

163

3. Alepas cornuta

165

4. Alepas tubulosa

169

Anelasma

169

1. Anelasma squalicola

170

Ibla

180

1. Ibla Cumingii

183

2. Ibla quadrivalvis

203

Scalpellum

215

Sub-Carinâ Nullâ

222

1. Scalpellum vulgare

222

2. Scalpellum ornatum

244

3. Scalpellum rutilum

253

Sub-Carinâ Presente

259

4. Scalpellum rostratum

259

5. Scalpellum Peronii

264

6. Scalpellum villosum

274

Pollicipes

293

1. Pollicipes cornucopia

298

2. Pollicipes elegans

304

3. Pollicipes polymerus

307

4. Pollicipes mitella

316

5. Pollicipes spinosus

324

6. Pollicipes sertus

327

Lithotrya

331

1. Lithotrya dorsalis

351

2. Lithotrya cauta

356

3. Lithotrya nicobarica

359

4. Lithotrya rhodiopus

363

5. Lithotrya truncata

366

6. Lithotrya Valentiana

371

THE

RAY SOCIETY.

INSTITUTED MDCCCXLIV.

LONDON.

MDCCCLI.

A MONOGRAPH

ON THE SUB-CLASS

CIRRIPEDIA,

WITH

FIGURES OF ALL THE SPECIES.

BY

CHARLES DARWIN, F.R.S., F.G.S.

THE LEPADIDÆ;

OR,

PEDUNCULATED CIRRIPEDES.

LONDON:
PRINTED FOR THE RAY SOCIETY.
MDCCCLI.

C. AND J. ADLARD, PRINTERS, BARTHOLOMEW

PREFACE.

My duty, in acknowledging the great obligations under which I lie to many naturalists, affords me most sincere pleasure. I had originally intended to have described only a single abnormal Cirripede, from the shores of South America, and was led, for the sake of comparison, to examine the internal parts of as many genera as I could procure. Under these circumstances, Mr. J. E. Gray, in the most disinterested manner, suggested to me making a Monograph on the entire class, although he himself had already collected materials for this same object. Furthermore, Mr. Gray most kindly gave me his strong support, when I applied to the Trustees of the British Museum for the use of the public collection; and I here most respectfully beg to offer my grateful acknowledgments to the Trustees, for their most liberal and unfettered permission of examining, and when necessary, disarticulating the specimens in the magnificent collection of Cirripedes, commenced by Dr. Leach, and steadily added to, during many years, by Mr. Gray. Considering the difficulty in determining the species in this class, had it not been for this most liberal permission by the Trustees, the public collection would have been of no use to me, or to any other naturalist, in systematically classifying the Cirripedes.

Previously to Mr. Gray suggesting to me the present Monograph, Mr. Stutchbury, of Bristol, had offered to intrust to me his truly beautiful collection, the fruit of many years' labour. At that time I refused this most generous offer, intending to confine myself to anatomical observations; but I have since accepted it, and still have the entire splendid collection for my free use. Mr. Stutchbury, with unwearied kindness, further supplied me with fresh specimens for dissection, and with much valuable information. At about the same period, Mr. Cuming strongly urged me to take up the subject, and his advice had more weight with me than that of almost any other person. He placed his whole magnificent collection at my disposal, and urged me to treat it as if it were my own: whenever I told him that I thought it necessary, he permitted me to open unique specimens of great value, and dissect the included animal. I shall always feel deeply honoured by the confidence reposed in me by Mr. Cuming and Mr. Stutchbury.

I lie under obligations to so many naturalists, that I am, in truth, at a loss how to express my gratitude. Mr. Peach, over and over again, sent me fresh specimens of several species, and more especially of Scalpellum vulgare, which were of invaluable assistance to me in making out the singular sexual relations in that species. Mr. Peach, furthermore, made for me observations on several living individuals. Mr. W. Thompson, the distinguished Natural Historian of Ireland, has sent me the finest collection of British species, and their varieties, which I have seen, together with many very valuable MS. observations, and the results of experiments. Prof. Owen procured for me the loan of some very interesting specimens in the College of Surgeons, and has always given me his invaluable advice and opinion, when consulted by me. Professor E. Forbes has been, as usual, most kind in obtaining for me specimens and information of all kinds. To the Rev. R. T. Lowe I am indebted for his particularly interesting collection of Cirripedes from the Island of Madeira—a collection offering a singular proof what treasures skill and industry can discover in the most confined locality. The well-known conchologist, Mr. J. G. Jeffreys, has sent for my examination a very fine collection of British specimens, together with a copious MS. list of synonyms, with the authorities quoted. To the kindness of Messrs. M^c Andrew, Lovell Reeve, G. Busk, G. B. Sowerby, Sen., D. Sharpe, Bowerbank, Hancock, Adam White, Dr. Baird, Sir John Richardson, and several other gentlemen, I am greatly indebted for specimens and information: to Mr. Hancock I am further indebted for several long and interesting letters on the burrowing of Cirripedes.

Nor are my obligations confined to British naturalists. Dr. Aug. Gould, of Boston, has most kindly transmitted to me some very interesting specimens; as has Prof. Agassiz other specimens collected by himself in the Southern States. To Mr. J. D. Dana, I am much indebted for several long letters, containing original and valuable information on points connected with the anatomy of the Cirripedia. To Mr. Conrad I am likewise indebted for information and assistance. Both the celebrated Professors, Milne Edwards and Müller, have lent me, from the great public collections under their charge, specimens which I should not otherwise have seen. To Professor W. Dunker, of Cassel, I am indebted for the examination of his whole collection. I have, in a former publication, expressed my thanks to Professor Steenstrup, but I must be permitted here to repeat them, for a truly valuable present of a specimen of the Anelasma squalicola of this work. I will conclude my thanks to all the above British and foreign naturalists, by stating my firm conviction, that if a person wants to ascertain how much true kindness exists amongst the disciples of Natural History, he should undertake, as I have done, a Monograph on some tribe of animals, and let his wish for assistance be generally known.

Had it not been for the Ray Society, I know not how the present volume could have been published; and therefore I beg to return my most sincere thanks to the Council of this distinguished Institution. To Mr. G. B. Sowerby, Junr., I am under obligations for the great care he has taken in making preparatory drawings, and in subsequently engraving them. I believe naturalists will find that the ten plates here given are faithful delineations of nature.

In Monographs, it is the usual and excellent custom to give a history of the subject, but this has been so fully done by Burmeister, in his 'Beiträge zur Naturgeschichte der Rankenfüsser,' and by M. G. Martin St. Ange, in his 'Mémoire sur l'Organisation des Cirripèdes,' that it would be superfluous here to repeat the same list of authors. I will only add, that since the date, 1834, of the above works, the only important papers with which I am acquainted, are, 1st. Dr. Coldstream 'On the Structure of the Shell in Sessile Cirripedes,' in the '

Encyclopædia

of Anatomy and Physiology;' 2d. Dr. Lovén 'On the Alepas squalicola,' ('Ofversigt of Kongl. Vetens.,' &c. Stockholm, 1844, p. 192,) giving a short but excellent account of this abnormal Cirripede; 3d. Professor Leidy's very interesting discovery, ('Proceedings of the Academy of Natural Sciences,' Philadelphia, vol. iv, No. I, Jan. 1848,) of eyes in a mature Balanus; 4th. Mr. A. Hancock's Memoir, ('Annals of Natural History, 2d series, Nov. 1849,) on his Alcippe lampas, the type of a new order of Cirripedes; 5th. Mr. Goodsir's Paper, ('Edinburgh New Philosoph. Journal,' July 1843,) on the Larvæ in the First Stage of Development in Balanus; 6th. Mr. C. Spence Bate's valuable Paper on the same subject, lately published, (Oct. 1851,) in the 'Annals of Natural History;' and lastly, M. Reinhardt has described, in the 'Copenhagen Journal of Natural History, Jan. 1851,' the Lithotrya nicobarica, and has discussed its powers of burrowing into rocks.

I have given the specific or diagnostic characters, deduced from the external parts alone, in both Latin and English. As I found, during the progress of this work, that a similarly abbreviated character of the softer internal parts, was very useful in discriminating the species, I have inserted it after the ordinary specific character.

In those cases in which a genus includes only a single species, I have followed the practice of some botanists, and given only the generic character, believing it to be impossible, before a second species is discovered, to know which characters will prove of specific, in contradistinction to generic, value.

In accordance with the Rules of the British Association, I have faithfully endeavoured to give to each species the first name attached to it, subsequently to the introduction of the binomial system, in 1758, in the tenth edition[1] of the 'Systema Naturæ.' In accordance with the Rules, I have rejected all names before this date, and all MS. names. In one single instance, for reasons fully assigned in the proper place, I have broken through the great law of priority. I have given much fewer synonyms than is usual in conchological works; this partly arises from my conviction that giving references to works, in which there is not any original matter, or in which the Plates are not of a high order of excellence, is absolutely injurious to the progress of natural history, and partly, from the impossibility of feeling certain to which species the short descriptions given in most works are applicable;—thus, to take the commonest species, the Lepas anatifera, I have not found a single description (with the exception of the anatomical description by M. Martin St. Ange) by which this species can be certainly discriminated from the almost equally common Lepas Hillii. I have, however, been fortunate in having been permitted to examine a considerable number of authentically named specimens, (to which I have attached the sign (!) used by botanists,) so that several of my synonyms are certainly correct.

[1] In the Rules published by the British Association, the 12th edition, (1766,) is specified, but I am informed by Mr. Strickland that this is an error, and that the binomial method was followed in the 10th edition.

The Lepadidæ, or pedunculated Cirripedes, have been neglected under a systematic point of view, to a degree which I cannot quite understand: no doubt they are subject to considerable variation, and as long as the internal surfaces of the valves and all the organs of the animal's body, are passed over as unimportant, there will occasionally be some difficulty in the identification of the several forms, and still more in settling the limits of the variability of the species. But I suspect the pedunculated Cirripedes have, in fact, been neglected owing to their close affinity, and the consequent necessity of their being included in the same Work with the Sessile Cirripedes; for these latter will ever present, I am fully convinced, insuperable difficulties in their identification by external characters alone.

I will here only further remark, that in the Introduction I have given my reasons for assigning distinct names to the several Valves, and to some parts of the included animal's body; and that in the Introductory Remarks, under the general description of the Lepadidæ, I have given an abstract of my Anatomical Observations.

CORRIGENDA AND ADDENDA.

Page

12, twenty lines from bottom, for "hinder pair of true thoracic limbs," read "pair of true thoracic limbs."

42, 43. I should have added, that the number of the segments in the cirri increases with the age of the specimen; but that the relative numbers in the different cirri keep, as far as I have seen, nearly constant; hence the numbers are often given in the descriptions.

99 et passim, for Pæcilasma, read Pœcilasma.

156. In a foot-note, I have alluded to a new genus of sessile Cirripedes, under the name of Siphonicella, I now find that this species has been called, by Professor Steenstrup, Xenobalanus globicipitis.

MONOGRAPH

ON

THE CIRRIPEDIA.

INTRODUCTION.

I should have been enabled to have made this Volume more complete, had I deferred its publication until I had finished my examination of all the other known Cirripedes; but my work would thus have been rendered inconveniently large. Until this examination is completed, it will be more prudent not to discuss, in detail, the position of the Lepadidæ amongst the Cirripedia, or of these latter in the great class of Crustacea, to which they now, by almost universal consent, have been assigned. I may, however, remark that I believe the Cirripedia do not approach, by a single character, any animal beyond the confines of the Crustacea: where such an approach has been imagined, it has been founded on erroneous observations; for instance, the closed tube within the stomach, described by M. Martin St. Ange (to whose excellent paper I am greatly indebted), as indicating an affinity to the Annelides, is, I am convinced, nothing but a strong epithelial lining, which I have often seen ejected with the excrement. Again, a most distinguished author has stated that the Cirripedia differ from the Crustacea:—1st. In having "a calcareous shell and true mantle;" but there is no essential difference, as shown by Burmeister, in the shells in these two classes; and Cirripedes certainly have no more claim to a mantle than have the bivalve entomostraca. 2d. "In the sexes joined in one individual;" but this, as we shall see, is not constant, nor of very much weight, even if constant. 3d. "In the body not being ringed;" but if the outer integument of the thorax of any Cirripede be well cleaned, it will be seen, (as was long ago shown by Martin St. Ange), to be most distinctly articulated. 4th. "In having salivary glands;" but these glands are, in truth, the ovaria. 5th. "In the liver being formed on the molluscous type;" I do not think this is the case, but I do not quite understand the point in question. 6th. "In not having a head or organs of sense;" this is singularly erroneous: Professor Leidy has shown the existence of eyes in the mature Cirripede; the antennæ, though preserved, certainly become functionless soon after the last metamorphosis; but there exist other organs of sense, which I believe serve for smelling and hearing: and lastly, so far from there being no head, the whole of the Cirripede externally visible, consists exclusively of the three anterior segments of the head.

The sub-class, Cirripedia, can be divided into three Orders; the first of which, mainly characterised by having six pair of thoracic cirri, includes all common Cirripedes: these latter may be divided into three families,—the Lepadidæ, or pedunculated Cirripedes, the subject of the present memoir; the Verrucidæ containing the single genus Verruca or Clisia; and, lastly, the Balanidæ, which consist of two very distinct sub-families, the Balaninæ and Chthamalinæ. Of the other two Orders above alluded to, one will, I believe, contain the remarkable burrowing genus Alcippe, lately described by Mr. Hancock, and a second burrowing genus, or rather family, obtained by me on the coast of South America. The third Order is highly singular, and differs as much from all other Cirripedes as does a Lernæa from other crustaceans; it has a suctorial mouth, but is destitute of an anus; it has not any limbs, and is as plainly articulated as the larva of a fly; it is entirely naked, without valves, carapace, or capitulum, and is attached to the Cirripede, in the sack of which it is parasitic, by two distinct threads, terminating in the usual larval, prehensile antennæ. I intend to call this Cirripede, Proteolepas. I mention it here for the sake of calling attention to any parasite at all answering to this description.

NOMENCLATURE OF THE VALVES.

Figure I. CAPITULUM.

Figure II. SCUTUM of LEPAS.

Figure III. TERGUM of LEPAS.

Although the present volume is strictly systematic, I will, under the general description of the Lepadidæ, give a very brief abstract of some of the most interesting points in their internal anatomy, and in the metamorphoses of the whole class, which I hope hereafter to treat, with the necessary illustrations, in detail. I enter on the subject of the metamorphoses the more readily, as by this means alone can the homologies of the different parts be clearly understood.

On the Names given to the different parts of Cirripedes.

I have unwillingly found it indispensable to give names to several valves, and to some few of the softer parts of Cirripedes. The accompanying figure of an imaginary Scalpellum includes every valve; the two most important valves of Lepas are also given, in which the direction of the lines of growth and general shape differ from those of Scalpellum as much as they do in any genus. The names which I have imposed will, I hope, be thus acquired without much difficulty.

Whoever will refer to the published descriptions of recent and fossil Cirripedia, will find the utmost confusion in the existing nomenclature: thus, the valve named in the woodcut the Scutum, has been designated by various well-known naturalists as the "ventral," the "anterior," the "inferior," the "ante-lateral," and the "latero-inferior" valve; the first two of these titles have, moreover, been applied to the rostrum or rostral valve of sessile Cirripedes. The Tergum has been called the "dorsal," the "posterior," the "superior," the "central," the "terminal," the "postero-lateral," and the "latero-superior" valve. The Carina has received the first two of these identical epithets, viz. the "dorsal" and the "posterior;" and likewise has been called the "keel-valve." The confusion, however, becomes far worse, when any individual valve is described, for the very same margin which is anterior or inferior in the eyes of one author, is the posterior or superior in those of another; it has often happened to me that I have been quite unable even to conjecture to which margin or part of a valve an author was referring. Moreover, the length of these double titles is inconvenient. Hence, as I have to describe all the recent and fossil species, I trust I may be thought justified in giving short names to each of the more important valves, these being common to the pedunculated and sessile Cirripedes.

The part supported by the peduncle, and which is generally, though not always, protected by valves, I have designated the Capitulum.

The title of Peduncle, which is either naked or squamiferous, requires no explanation; the scales on it, and the lower valves of the capitulum, are arranged in whorls, which, in the Latin specific descriptions, I have called by the botanical term of verticillus.

I have applied the term Scutum to the most important and persistent of the valves, and which can generally be recognised by the hollow giving attachment to the adductor scutorum muscle, from the resemblance which the two valves taken together bear to a shield, and from their office of protecting the front side of the body. From the protection afforded by the two Terga to the dorso-lateral surface of the animal, these valves have been thus called. The term Carina[2] is a mere translation of the name already used by some authors, of Keel-Valve.

[2] In the Carina of Fossil Species of Scalpellum, I have found it necessary to distinguish different parts, viz., A, the tectum, of which half is seen; B, the parietes; and C, the intra-parietes.

The Rostrum has been so called from its relative position to the carina or keel. There is often a Sub-carina and a Sub-rostrum.

The remaining valves, when present, have been called Latera; there is always one large upper one inserted between the lower halves of the scuta and terga, and this I have named the Upper Latus or Latera; the other latera in Pollicipes are numerous, and require no special names; in Scalpellum, where there are at most only three pair beneath the Upper Latera, it is convenient to speak of them (vide Woodcut, I,) as the Carinal, Infra-median, and Rostral Latera.

As each valve often requires (especially amongst the fossil species) a distinct description, I have found it indispensable to give names to each margin. These have mostly been taken from the name of the adjoining valve, (see fig. I.) In Lepas, Pollicipes, &c., the margin of the scutum adjoining the tergum and upper latus, is not divided (fig. II) into two distinct lines, as it is in Scalpellum, and is therefore called the Tergo-lateral margin. In Scalpellum (fig. I) these two margins are separately named Tergal and Lateral. The angle formed by the meeting of the basal and lateral or tergo-lateral margins, I call the Baso-lateral angle; that formed by the basal and occludent margins, I call, from its closeness to the Rostrum, the Rostral angle. In Pollicipes the carinal margin of the tergum can be divided into an upper and lower carinal margin; of this there is only a trace (fig. I) in Scalpellum.

That margin in the scuta and terga which opens and shuts for the exsertion and retraction of the cirri, I have called the Occludent margin. In the terga of Lepas (fig. III) and some other genera, the occludent margin is highly protuberant and arched, or even formed of two distinct sides.

Occasionally, I have referred to what I have called the primordial valves: these are not calcified; they are formed at the first exuviation, when the larval integuments are shed: in mature Cirripedes they are always seated, when not worn away, on the umbones of the valves.

The membrane connecting the valves, and forming the peduncle, and sometimes in a harder condition replacing the valves, I have often found it convenient to designate by its proper chemical name of Chitine, instead of by horny, or other such equivalents. When this membrane at any articulation sends in rigid projections or crests, for the attachment of muscles or any other purpose, I call them, after Audouin, apodemes. For the underlying true skin, I use the term corium.

The animal's body is included within the capitulum, within what I call the sack (see Pl. IV, figs. 2 and 8´ a, and Pl. IX, fig. 4). The body consists of the thorax supporting the cirri, and of an especial enlargement, or downward prolongation of the thorax, which includes the stomach, and which I have called the prosoma. (Pl. IX, fig. 4 n). The cirri are composed of two arms or rami, supported on a common segment or support, which I call the pedicel. The caudal appendages are two little projections, either uni-or multi-articulate (Pl. IV, fig. 8´ a), on each side of the anus, and just above the long proboscis-like penis. On the thorax and prosoma, or on the pedicels of the cirri, there are in several genera, long, thin, tapering filaments, which have generally been supposed to serve as branchiæ; these I call simply filaments, or filamentary appendages (Pl. IX, fig. 4 g-l). The mouth (fig. 4 b) is prominent, and consists of palpi soldered to the labrum; mandibles, maxillæ, and outer maxillæ, these latter serve as an under lip; to these several organs I sometimes apply the title used by Entomologists, of "trophi." Beneath the outer maxillæ, there are either two simple orifices or tubular projections; these, I believe, serve as organs of smell, and have hence called them the olfactory orifices. Within the sack, there are often two sheets of ova (Pl. IV, fig. 2 b), these I call (after Steenstrup, and other authors) the ovigerous Lamellæ; they are united to two little folds of skin (Pl. IV, fig. 2 f), which I call the ovigerous Fræna.

From the peculiar curved position which the animal's body occupies within the capitulum, I have found it far more convenient (not to mention the confusion of nomenclature already existing) to apply the term Rostral instead of ventral, and Carinal instead of dorsal, to almost all the external and internal parts of the animal. Cirripedes have generally been figured with their surfaces of attachment downwards, hence I speak of the lower or Basal margins and angles, and of those pointing in an opposite direction as the Upper; strictly speaking, as we shall presently see, the exact centre of the usually broad and flat surface of attachment is the anterior end of the animal, and the upper tips of the Terga, the posterior end of that part of the animal which is externally visible; but in some cases, for instance in Coronula, where the base is deeply concave, and where the width of the shell far exceeds the depth, it seemed almost ridiculous to call this, the anterior extremity; as likewise does it in Balanus to call the united tips of the Terga, lying deeply within the shell, the most posterior point of the animal, as seen externally.

I have followed the example of Botanists, and added the interjection [!] to synonyms, when I have seen an authentic specimen bearing the name in question.

Every locality, under each species, is given from specimens ticketed in a manner and under circumstances appearing to me worthy of full confidence,—the specific determination being in each case made by myself.

Class—CRUSTACEA. Sub-Class—CIRRIPEDIA.

Family—LEPADIDÆ.

Cirripedia pedunculo flexili, musculis instructo: scutis[3] musculo adductore solummodô instructis: valvis cæteris, siquæ adsunt, in annulum immobilem haud conjunctis.

Cirripedia having a peduncle, flexible, and provided with muscles. Scuta[3] furnished only with an adductor muscle: other valves, when present, not united into an immovable ring.

[3] The meaning of this and all other terms is given in the Introduction, at pp. 3-7.

Metamorphoses; larva, first stage, pp. 9-12; larva, second stage, p. 13; larva, last stage, p. 14; its carapace, ib.; acoustic organs, p. 15; antennæ, ib.; eyes, p. 16; mouth, p. 17; thorax and limbs, p. 18; abdomen, p. 19; viscera, ib.; immature cirripede, p. 20; homologies of parts, p. 25.

Description of mature Lepadidæ, p. 28; capitulum, ib.; peduncle, p. 31; attachment, p. 33; filamentary appendages, p. 38; shape of body, and muscular system, p. 39; mouth, ib.; cirri, p. 42; caudal appendages, p. 43; alimentary canal, 44; circulatory system, p. 46; nervous system, ib.; eyes, p. 49; olfactory organs, p. 52; acoustic(?) organs, p. 53; male sexual organs, p. 55; female organs, p. 56; ovigerous lamellæ, p. 58; ovigerous fræna, ib.; exuviation, p. 61; rate of growth, ib.; size, ib.; affinities of family, p. 64; range and habitats, p. 65; geological history, p. 66.

Metamorphoses.—I will here briefly describe the Metamorphoses, as far as known, common to all Cirripedia, but more especially in relation to the present family. I may premise, that since Vaughan Thompson's capital discovery of the larvæ in the last stage of development in Balanus, much has been done on this subject: this same author subsequently published[4] in the 'Philosophical Transactions,' an account of the larvæ of Lepas and Conchoderma (Cineras) in the first stage; and seeing how totally distinct they were from the larva of the latter stage in Balanus, he erroneously attributed the difference to the difference in the two families, instead of to the stage of development. Burmeister[5] first showed, and the discovery is an important one, that in Lepas the larvæ pass through two totally different stages. This has subsequently been proved by implication to be the case in Balanus, by Goodsir,[6] who has given excellent drawings of the larva in the first stage; and quite lately, Mr. C. Spence Bate, of Swansea, has made other detailed observations and drawings of the larvæ of five species in this same early stage, and has most kindly permitted me to quote from his unpublished paper[7]. I am enabled to confirm and generalise these observations, in all the Cirripedes in the Order containing the Balanidæ and Lepadidæ.

[4] Philosophical Transactions, 1835, p. 355, Pl. vi.

[5] Beiträge zur Naturgeschichte der Rankenfüsser, 1834. Mr. J. E. Gray, however, briefly described, in 1833, (Proceedings, Zoological Society, October,) the larva in the first stage of Balanus; in this notice the anterior end of the larva is described as the posterior.

[6] Edinburgh New Philosophical Journal, July 1843, Pls. iii and iv.

[7] This will appear in the October number (1851) of the 'Annals of Natural History.'

The ova, and consequently the larvæ of the Lepadidæ, in the First Stage, whilst within the sack of the parent, vary in length from .007 to .009 in Lepas, to .023 of an inch in Scalpellum: my chief examination of these larvæ has been confined to those of Scalpellum vulgare; but I saw them in all the other genera. The larva is somewhat depressed, but nearly globular; the carapace anteriorly is truncated, with lateral horns; the sternal surface is flat and broad, and formed of thinner membrane than the dorsal. The horns just alluded to are long in Lepas and short in Scalpellum; their ends are either rounded and excessively transparent, or, as in Ibla, furnished with an abrupt, minute, sharp point: within these horns, I distinctly saw a long filiformed organ, bearing excessively fine hairs in lines, so exactly like the long plumose spines on the prehensile antennæ of the larvæ in the last stage; that I have not the least doubt, that these horns are the cases in which antennæ are in process of formation. Posteriorly to them, on the sternal surface, near each other, there are two other minute, doubly curved, pointed horns, about .004 in length, directed posteriorly; and within these I again saw a most delicate articulated filiformed organ on a thicker pedicel: in an excellent drawing, by Mr. C. S. Bate, of the larva of a Chthamalus (Balanus punctatus of British authors), after having kept alive and moulted once, these organs are distinctly shown as articulated antennæ (without a case), directed forwards: hence, before the first moult in Scalpellum, we have two pair of antennæ in process of formation. Anteriorly to the bases of these smaller antennæ is seated the heart-shaped eye, (as I believe it to be,) .001 in diameter, with apparently a single lens, surrounded, except at the apex, by dark-reddish pigment-cells. In some cases, as in some species of Lepas, the larvæ, when first excluded from the egg, have not an eye, or a very imperfect one.

There are three pairs of limbs, seated close together in a longitudinal line, but some way apart in a transverse direction: the first pair always consists of a single spinose ramus, it is not articulated in Scalpellum, but is multi-articulate in some genera; it is directed forwards. The other two pair have each two rami, supported on a common haunch or pedicel: in both pair, the longer ramus is multi-articulate, and the shorter ramus is without articulations, or with only traces of them: the longer spines borne on these limbs (at least, in Scalpellum and Chthamalus,) are finely plumose. The abdomen terminates, a little beyond the posterior end of the carapace, in a slightly upturned horny point; a short distance anteriorly to this point, a strong, spinose, forked projection depends from the abdominal surface.

Messrs. V. Thompson, Goodsir, and Bate, have kept alive for several days the larvæ of Lepas, Conchoderma, Balanus, Verruca, and Chthamalus, and have described the changes which supervene between the first and third exuviations. The most conspicuous new character is the great elongation of the posterior point of the carapace into an almost filiform, spinose point in Lepas, Conchoderma, Chthamalus, and Balanus, but not according to Goodsir, in one of the species of the latter genus. The posterior point, also, of the abdomen becomes developed in Balanus (Goodsir) into two very long, spear-like processes, serrated on their outer sides; in Lepas and Conchoderma, according to Thompson, into a single, tapering spinose projection; and in Chthamalus, as figured by Mr. Bate, the posterior bifid point, as well as the depending ventral fork, increase much in size. Another important change, which has been particularly attended to by Mr. Bate, is the appearance of spinose projections and spines (some of which are thick, curved, and strongly plumose, or, almost pectinated along their inner sides) on the pedicels and lower segments of the shorter rami of the two posterior pairs of limbs.

The mouth in its earliest condition alone remains to be described; in S. vulgare, it is seated on a very slight prominence, in a most remarkable situation, namely, in a central point between the bases of the three pairs of legs. I traced by dissection the œsophagus for some little way, until lost in the cellular and oily matter filling the whole animal, and it was directed anteriorly, which is the direction that might have been expected, from the course followed by the œsophagus in the larva in the last stage, and in mature Cirripedes. Mr. A. Hancock has called my attention to a probosciformed projection on the under side of the larva of Lepas fascicularis, when just escaped from the egg. Mr. Bate has described this same proboscis in Balanus and Chthamalus, and states the important fact, that it is capable of being moved by the animal; and, lastly, I have seen it in an Australian Chthamalus, and in Ibla, of remarkable size. This proboscis, which is always directed posteriorly, (like the mouth in the mature animal,) certainly answers to the mouth as made out by dissection in Scalpellum; and I believe I saw, as has Mr. Bate, a terminal orifice: it certainly does not possess any trophi. In Ibla (in which the larva is large enough for dissection), the base of the proboscis arises posteriorly to the first pair of legs, and the orifice at the other end reaches beyond or posteriorly to the point, where the mouth in Scalpellum opens, namely between the middle pair of legs. The mouth being either so largely probosciformed or seated only on a slight eminence, in two genera so closely allied as Ibla and Scalpellum, and (judging from Mr. Thompson's figures, and from what I have seen myself,) in the species of the same genus Lepas, is a singular difference: in the cases in which, at first, the proboscis is absent, it would probably soon be developed. I cannot but suppose that the inwardly directed spines on the bases of the two posterior legs, which are so rapidly developed, serve some important end, namely, as organs of prehension for the larvæ, like the mandibles and maxillæ of mature Cirripedes, for seizing their prey, and conveying it to their moveable mouths, conveniently seated for this purpose.

The first pair of legs answers, as I believe from reasons hereafter to be assigned, to the outer pair of maxillipods in the higher crustacea; and the other four legs to the first two pair of thoracic limbs in these same crustacea; this being the case, the highly remarkable position of the mouth in the larva, either between the bases of the two posterior pair of legs, or at least posteriorly to the first pair, together with the probable functions of the spiny points springing from the basal segments of the two hinder pair of true thoracic limbs, forcibly bring to mind the anomalous structure of the mouth being situated in the middle of the under side of the thorax, in Limulus,—that most ancient of crustaceans, and therefore one likely to exhibit a structure now embryonic in other orders. I will only further remark, that I suspect that the truncation of the anterior end of the carapace, has been effected by the segments having been driven inwards, and consequently, that the larger antennæ within the lateral horns, though standing more in front than the little approximate pair, are normally the posterior of the two pair. According to Milne Edwards, the posterior pair are normally seated outside the anterior pair, and this is the case with those within the lateral horns.

Larva in the Second Stage.—Notwithstanding the considerable changes, already briefly given, which the larva undergoes during the first two or three exuviations after leaving the egg, all these forms may be conveniently classed under the first stage. The larva in the Second stage is known only from a single specimen described, figured, and found by Burmeister,[8] adhering to sea-weed in the midst of other larvæ of Lepas in the last stage. In its general shape and compressed form, it seems to come nearer to the last than to the first stage. It has only three pair of legs, situated much more posteriorly on the body than in the first stage, and all directed posteriorly; they are much shorter than heretofore, and resemble rather closely those of the last stage, with the important exception that the first pair has only one ramus. It is this circumstance which leaves no doubt on my mind, that we here have the three pair of limbs, of the first stage, metamorphosed. The body is prolonged some way behind these limbs, and ends in a blunt, rounded point, in which, probably, are developed the three posterior pair of legs and the abdomen of the larva in the last stage. The mouth is now seated some way anteriorly to the limbs, is large and probosciformed, and is, I presume, still destitute of trophi. There are now two closely approximate eyes, but as yet both are simple. The smaller pair of antennæ has disappeared. The whole animal was attached to the sea-weed by a (I presume, pair of,) "fleischigen Fortsatz," which Burmeister considers as the prehensile antennæ, to be presently described, in an early state of development. I have little doubt that this is correct, for in an abnormal Cirripede of another order, in which the larva appears in the first stage with prehensile antennæ, the eggs have two great projecting horns including these organs, and attached by their tips, through some unknown means, to the sack of the parent, apparently in the same manner as Burmeister's larva was attached to the sea-weed. I will only further remark on the larva of this Second stage, that its chief development since the first stage, has been towards its anterior end. The next great development, to be immediately described, is towards the posterior end of the animal.

[8] Beiträge zur Naturgeschichte der Rankenfüsser, s. 16, Tab. i, figs. 3, 4.

Larva, Last Stage.—My chief examination has been directed, at this stage of development, to the larvæ of Lepas australis, which are of unusual size, namely, from .065 to even almost .1 of an inch in length; I examined, however, the larvæ of several other species of Lepas, of Ibla and of Balanus, with less care, but sufficiently to show that in all essential points of organisation they were identical; this, indeed, might have been inferred from the similarity of the larval prehensile antennæ, preserved in the bases of all mature Cirripedes, and which I have carefully inspected in almost every genus. The larvæ in this final stage, in most of the genera, have increased many times in size since their exclusion from the egg; for instance, in Lepas australis, from .007 to .065, or even to .1 of an inch. They are now much compressed, nearly of the shape of a cypris or mussel-shell, with the anterior end the thickest, the sternal surface nearly or quite straight, and the dorsal arched. Almost the whole of what is externally visible consists of the carapace; for the thorax and limbs are hidden and enclosed by its backward prolongation; and even at the anterior end of the animal, the narrow sternal surface can be drawn up, so as to be likewise enclosed. As in several Stomapod crustaceans, the part of the head bearing the antennæ and organs of sense, in front of the mouth, equals, or even exceeds in length, and more than exceeds in bulk, the posterior part of the body, consisting of the enclosed thorax and abdomen. I will now briefly describe, in the following order, the carapace, the organs of sense, mouth, thorax and limbs, abdomen, and internal viscera.

The form of the Carapace has been sufficiently described; it consists of thick chitine membrane, marked with lines, and sometimes with stars and other patterns; it is obscurely divided into two halves by a line or suture along part of the dorsal margin; these halves or two valves are drawn together by an adductor muscle, in the same relative position as in the mature Cirripede. The part overhanging and enclosing the thorax is lined by an excessively delicate membrane, obviously homologous with the lining of the sack in the mature animal, and is nothing but a duplicature of the carapace, rendered very thin from being on the under or protected side: a layer of true skin or corium, probably double, separates these two folds.

Acoustic Organs.—On the borders of the carapace, at the anterior end, on the sternal surface, there are two minute orifices, in L. australis .002 in diameter, sometimes having a distinct border round them; the membrane of the carapace on the inside is prolonged upwards and inwards in two short funnel-shaped tubes, lodged in closed sacks of the corium: within these sacks on each side a delicate bag is suspended, and hangs in the mouth of the above funnel; at the upper end a large nerve could be distinctly seen to enter the bag: I cannot doubt that this is a sense-organ; from its position and from the animal not feeding (as we shall presently see), I conclude that it is an acoustic organ.

Antennæ.—These are large and conspicuous; they are attached very obliquely on the sternal surface, a little way from the anterior end of the carapace, beyond which, when exserted, they extend;[9] they can (at least in Ibla) be retracted within the carapace. They consist of three segments: the first or basal one is much larger than the others, and apparently always has a single spine on the outer distal margin. The second segment consists either of a large, thin, circular, sucking disc, or is hoof-like (Tab. V, figs. 5, 10, 11, 12); in all cases it is furnished with one or more spines, (seven very long ones in Lepas,) on the exterior-hinder margin. The third and ultimate segment is small; it is articulated on the upper surface of the disc, and is directed rectangularly outwards; it is sometimes notched, and even shows traces of being bifid; it bears about seven spines at the end; some of these spines are hooked, others simple, and in Lepas and Conchoderma, two or three are very long, highly flexible, and plumose, a double row of excessively fine hairs being articulated on them. I can hardly doubt that these latter spines, (within which the purple corium could be seen to enter a little way,) floating laterally outwards, serve as feelers. The antennæ, at first, are well furnished with muscles. They serve, in Lepas, according to Mr. King, and in Balanus, according to Mr. Bate, and as I saw myself in another unnamed order, for the purpose of walking, one limb being stretched out before the other; but their main function is to attach the larva for its final metamorphosis into a Cirripede. The disc can adhere even to so smooth a surface as a glass tumbler.[10] The attachment is at first manifestly voluntary, but soon becomes involuntary and permanent, being effected by special and most remarkable means, which will be most conveniently described in a later part of this Introduction. I will here only state that I traced with ease the two cement-ducts running from two large glandular bodies, to within the antennæ up to the discs.

[9] Mr. J. D. Dana, who has examined these organs in the larvæ of Lepas, informs me in a letter, that in his opinion they "correspond with the inferior antennæ, the superior being wanting, as in most Daphnidæ." He continues—"I know of no case in which the inferior are obsolete when the superior are developed; but the reverse is often true." In position these antennæ certainly correspond to the inferior and central pair of the larva in the first stage, which belong, as it would appear, to the first segment of the body; but judging from the drawing by Burmeister of the larva in the second stage, I am, in some respects, more inclined to consider that they correspond to the larger pair seen within the lateral horns of the carapace in the first stage.

[10] Rev. B. L. King. Annual Report of B. Institution of Cornwall, 1848, p. 55.

Eyes.—Close behind the basal articulations of the antennæ, the sternal surface consists of two approximate, elongated, narrow, flat pieces, or segments. These Burmeister considers as the basal segments of the antennæ: as they are not cylindrical, I do not see the grounds for this conclusion: their posterior ends are rounded, and the membrane forming them is reflected inwards, in the form of two, forked, horny apodemes, together resembling two letters, UU, close together; these project up, inside the animal, for at least one third of its thickness from the sternal to the dorsal surface. The two great, almost spherical eyes in L. australis, each 1/150th of an inch in diameter, are attached to the outer arms, thus, °UU°, in the position of the two full stops. Hence the eyes are included within the carapace. Each eye consists of eight or ten lenses, varying in diameter in the same individual from 1/2000 to 3/2000th of an inch, enclosed in a common membranous bag or cornea, and thus attached to the outer apodemes. The lenses are surrounded half way up by a layer of dark pigment-cells. The nerve does not enter the bluntly-pointed basal end of the common eye, but on one side of the apodeme. The structure here described is exactly that found, according to Milne Edwards, in certain crustacea. In specimens just attached, in which no absorption has taken place, two long muscles with transverse striæ may be found attached to the knobbed tips of the two middle arms of the two °UU°, and running up to the antero-dorsal surface of the carapace, where they are attached; other muscles (without transverse striæ) are attached round the bases, on both sides of both forks. The action of these muscles would inevitably move the eyes, but I suspect that their function may be to draw up the narrow, deeply folded, sternal surface, and thus cause the retraction of the great prehensile antennæ within the carapace.

Mouth.—This is seated in exactly the same position as in the mature Cirripede, on a slight prominence, fronting the thoracic limbs, and so far within the carapace, that it was obviously quite unfitted for the seizure of prey; and it was equally obvious, that the limbs were natatory, and incapable of carrying food to the mouth. This enigma was at once explained by an examination of the mouth, which was found to be in a rudimentary condition and absolutely closed, so that there would be no use in prey being seized. Underneath this slightly prominent and closed mouth, I found all the masticatory organs of a Cirripede, in an immature condition. The state of the mouth will be at once understood, if we suppose very fluid matter to be poured over the protuberant mouth of a Cirripede, so as to run a little way down, in the shape of internal crests, between the different parts, and in the shape of a short, shrivelled, certainly closed tube, a little way (.008 of an inch in L. australis) down the œsophagus. Hence, the larva in this, its last stage, cannot eat; it may be called a locomotive Pupa;[11] its whole organisation is apparently adapted for the one great end of finding a proper site for its attachment and final metamorphosis.

[11] M. Dujardin has lately ('Comptes Rendus,' Feb. 5, 1850, as cited in 'Annals of Nat. History,' vol. v, p. 318,) discovered that the "Hypopi are Acari with eight feet, without either mouth or intestine, and which, being deprived of all means of alimentation, fix themselves at will, so as to undergo a final metamorphosis, and they become Gamasi or Uropodi." Here, then, we have an almost exactly analogous case. M. Dujardin asks—"Ought, therefore, the Hypopi to be called larvæ, when, under that denomination, have hitherto been comprised animals capable of nourishing themselves?"

Thorax and Limbs.—The thorax is much compressed, and consists of six segments, corresponding with the six pair of natatory legs; the anterior segments are much plainer (even the first being distinctly separated by a fold from the mouth), than the posterior segments, which is exactly the reverse of what takes place in the mature Cirripede; in the latter, the first segment is confounded with the part bearing the mouth. The epimeral elements of the thorax are distinguishable; the sternal surface is very narrow, and is covered with complicated folds and ridges. The six pair of legs are all close, one behind the other, and all are alike in having a haunch or pedicel of two segments, directed forwards, bearing two arms or rami, each composed of two segments, the outer ramus being a little longer than the inner one. On the lower segments in both rami of all the limbs, there is a single spine. In all the limbs, the obliquely truncated summit of the terminal segment of the inner ramus bears three very long, beautifully plumose spines: in the first pair, the summit of the outer ramus bears four, and in the five succeeding pair, six similar spines. This difference, small as it is, is interesting, as recalling the much greater difference between the first and succeeding pairs, in the first and second stage of development. The terminal segments of all the rami, bearing the long plumose spines, are directed backwards. The limbs and thorax are well furnished with striated muscles. The animal, according to Mr. King, swims with great rapidity, back downwards. The limbs can be withdrawn within the carapace.

Abdomen and Caudal Appendages.—The abdomen is small, and its structure might easily be overlooked without careful dissection of the different parts: it consists of three segments; the first can be seen to be distinct from the last thoracic segment, bearing the sixth pair of limbs, only from the fold of the epimeral element, and from its difference in shape; the second segment is very short, but quite distinct; the third is four or five times as long as the second, and bears at the end two little appendages, each consisting of two segments, the lower one with a single spine, and the upper one with three, very long, plumose spines, like those on the rami of the thoracic limbs. The abdomen contains only the rectum and two delicate muscles running into the two appendages, between the bases of which the anus is seated.

Internal Viscera.—Within the body, in front of the mouth, it was easy to find the stomach (with two pear-shaped cæca at the upper end), running first anteriorly, and then curving back and reaching the anus by a long rectum, difficult to be followed: it appeared, however, to me, that this stomach had more relation to the young Cirripede, of which every part could now generally be traced, than to the larva, with its closed and rudimentary mouth: the fact, however, of its being prolonged to the anus, which is in a different position in the larva and mature state, shows that the stomach serves, at least, as an excretory channel. Besides the stomach, the several muscles already alluded to, and much pulpy and oily matter, the only other internal organs consist of two long, rather thick, gut-formed masses, into the anterior ends of which the cement-ducts running from the prehensile antennæ could be traced. These masses are formed of irregular orange balls, about .001 of an inch in diameter, made up of rather large cells, so to have a grape-like appearance, held together by a transparent pale yellowish substance, but apparently not enclosed in a membrane: these masses lie rather obliquely, and approach each other at their anterior ends; they extend from above the compound eyes, to the cæca of the stomach to which they cohere, but in young specimens, they extend some way beyond the cæca, between the folds of the carapace. The two cement-ducts, at the points where they enter these bodies, expand and are lost; at this point, also, the little orange-coloured masses of cells have the appearance of being broken down into a finer substance. Within the cement-ducts I saw a distinct chord of rather opaque cellular matter. We shall presently see, that these gut-formed masses are the incipient ovaria.

The Young Cirripede within the Larva.—Several times I succeeded in dissecting off the integuments of the lately-attached larva, and in displaying the young Lepas australis entire. The following description applies to the Cirripede in this state; but for convenience sake, I shall occasionally refer to its condition when a little more advanced. I may premise, and the fact in itself is curious, that the bivalve-like shell of the larva, together with the compound eyes, is first moulted, and some time afterwards, the inner lining of the sack, together with the integuments of the thorax and of the natatory legs: hence, I often found specimens, which externally seemed to have perfected their metamorphoses, but which, within their sacks, retained all the characters of the natatory larva. According to Mr. King, the larva of Lepas throws off its external shell five days after becoming attached. Whilst the young Lepas is closely packed within the larva, the capitulum, as known by the five valves, about equals in length the peduncle. The peduncle occupies the anterior half of the larva; when fully stretched, it becomes narrower and slightly longer than the capitulum; the separation between the capitulum and peduncle is almost arbitrary in the mature animal, and corresponds with no particular line in the larva. Even at this early period, the muscles of the peduncle are quite distinct. No vestige is preserved in the outer integument, of the sternal and dorsal sutures of the larval carapace; but in the corium of the peduncle, three coloured marks which occur near the eyes, and two little curled marks which occur near the acoustic orifices of the larva, are all preserved for some time after maturity. The compound eyes, as we have seen, are attached to apodemes, springing from the sternal surface of the larval carapace, and are consequently cast off with it: whilst the young Cirripede is packed within the larva, the outer integument of its peduncle necessarily forms a deep transverse fold passing over the eyes and apodemes, and this, as we shall presently see, plays an important part in the future position of the animal. The antennæ are not moulted with the carapace, but left cemented to the surface of attachment; their muscles are converted into sinewy fibres, the corium after a short period is absorbed, and they are then preserved in a functionless condition. No trace of the two acoustic sacks can be perceived in the corium of the young Cirripede, excepting the coloured marks above alluded to.

In the young capitulum, the five valves stand some way apart from each other; they are elegant objects under the microscope; they are not calcified, but consist exclusively of chitine; they are rather thick, composed of an outer membrane lined by hexagonal prisms, quite unlike any other membrane in the animal. These valves, which I have called primordial valves, resemble pretty closely in shape the valves of the mature animal; the fork of the carina, however, is indicated only by a slight constriction above the lower end. After the exuviation of the larval integuments, and when calcification commences, the first layer of shell is deposited under, and then round these primordial valves. The latter, in well preserved old specimens, may often be detected on the umbones of the scuta, terga, and carina, but not on the umbones of any other valves.

The mouth seems one of the earliest parts developed: in the youngest larva dissected, I could make out at least points corresponding with each organ; and, at the period when the young Cirripede could be dissected out of its larval envelopes, their general details were quite plain. The labrum, however, had not become bullate. The mouth, as we have seen, is formed under the rudimentary mouth of the larva, and at the same relative spot occupied by the probosciformed mouth of the larva in the second stage. Thus far, in the young Cirripede and larva, there has been no great change in the relative positions of the parts: the rudimentary eyes, however, of the former are developed posteriorly to (or above, as applied to a Cirripede,) the cast-off compound eyes of the larva; but the position of the mouth, of the antennæ, and of the several coloured marks in the corium, prove to demonstration, the correspondence in both of part to part. The case is rather different with what follows.

The Cirri are developed at first of considerable length, so that the young animal may soon provide itself with food; in Lepas australis they are of great length, the sixth pair consisting of seventeen or eighteen obscure segments. The extreme tips of the twenty-four rami of the six pair of cirri, are formed within the twenty-four, corresponding, little, bi-segmental rami of the six pair of natatory legs; but as the cirri are many times longer than these legs, they occupy in a bundle the whole thorax of the larva; no part whatever of the thorax of the Cirripede is formed within the thorax of the larva, but (together with the pedicels of the anterior cirri) within the cephalic cavity. As a consequence of this, the longitudinal axis of the thorax of the young Cirripede lies almost transversely to the longitudinal axis of the larva; and the Cirripede, from this transverse position of its thorax, comes to be, as it were, internally, almost cut in twain, and the sack thus produced. As soon as the young Cirripede is free and can move itself, the cirri are curled up, and the thorax is advanced towards the orifice of the capitulum, its longitudinal axis resuming the position of approximate parallelism to the longitudinal axis of the whole body, which it had in the larval condition. The reader will, perhaps, understand what I mean, if he will look at the mature Cirripede, figured in Pl. IX, fig. 4. In this, he will see that the body or thorax is united to the peduncle only by a small part below the mouth; on the other hand, if he imagines the whole bottom of the body (as high up as the letter h) united and blended into the peduncle, he will see the state in which these parts exist in the larva. Now, let him greatly shorten the cirri, so as to resemble the natatory legs of the larva, and then imagine a young Cirripede, with cirri of full length, formed within the old one, he will see that the new thorax supporting the cirri will have to be developed in an almost transverse position,—the animal consequently being internally almost separated into twain.

Of the internal organs, whilst the Cirripede is still within the larva, I have already mentioned the stomach with its pair of cæca: from the retracted position of the thorax and rudimentary abdomen, and consequently of the anus, compared with these parts in the larva, the alimentary canal is not above half its former length. There is, as yet, no trace of the filaments supposed by some to act as branchiæ, at the base of the first pair of cirri. Nor could I perceive a trace of the testes or vesiculæ seminales: the penis is represented by a minute, apparently imperforate projection. I have already briefly described the pair of large, gut-formed bodies in the larva, into the anterior ends of which the cement-ducts ran, and evidently derived their slightly opaque, cellular contents. At a very early age, before the young Cirripede can be distinctly made out, the posterior ends of these gut-formed bodies are absorbed, so as not to pass beyond the cæca of the stomach. When the young Cirripede is plainly developed within the larva, these bodies in a relatively reduced condition are still distinct near the cæca, and at the opposite or anterior end (i. e. lower, in the position in which Cirripedes are usually figured), they have branched out into a sheet of delicate inosculating tubes; these could be traced by every stage, until, in the young perfected Cirripede, they filled the peduncle as ordinary ovarian tubes. In the larva, the two gut-formed bodies or incipient ovaria keep of equal thickness from one to the other end, but in the mature Cirripede, the ovarian tubes in the peduncle and the small, glandular, grape-like masses, near the stomach-cæca, are connected only by a delicate tube; this I failed in tracing in specimens in the very immature condition of those now under description.

The larva fixes itself with its sternal surface parallel and close to the surface of attachment, and the antennæ become cemented to it: if the Cirripede, after its metamorphosis had remained in this position, the cirri could not have been exserted, or only against the surface of attachment; but there is a special provision, that the young Cirripede shall immediately assume its proper position at right angles to the position which it held whilst within the larva, namely with its posterior end upwards. This is effected in a singular manner by the exuviation of the great compound eyes, which we have seen are fastened to the outer arms of the double °UU°-like, sternal apodemes: these together with the eyes stretch transversely across, and internally far up into, the body of the larva; and, as the whole has to be rejected or moulted, the membrane of the peduncle of the young Cirripede has necessarily to be formed with a wide and deep inward fold, extending transversely across it; this when stretched open, after the exuviation of the larval carapace and apodemes, necessarily causes the sternal side of the peduncle to be longer than the dorsal, and, as a consequence, gives to the young Cirripede its normal position, at right angles to that of the larva when first attached.

I may here state, that I have examined the larvæ in this the final or perfect stage in four species of Lepas, in Conchodermavirgata, Ibla quadrivalvis, and, though rather less minutely, in Balanus balanoides, and I find all essential points of organisation similar. With the exception of diversities in the proportional sizes of the different parts, and in the patterns on the carapace, the differences, even in the arrangement of the spines on the limbs and antennæ, are less than I should have anticipated.

I have in this abstract treated the metamorphoses at greater length than I should otherwise have done, on account of the great importance of arriving at a correct homological interpretation of the different parts of the mature animal. In Crustacea, according to the ordinary view, there are twenty-one segments; of these I can recognise in the Cirripede, on evidence as good as can generally be obtained, all with the exception of the four terminal abdominal segments; these do not occur in any species known to me, in any stage of its development. If that part of the larva in front of the mouth, bearing the eyes, the prehensile antennæ, and in an earlier stage two pair of antennæ, be formed, as is admitted in all other Crustacea, of three segments, then beyond a doubt, from the absolute correspondence of every part, and even every coloured mark, the peduncle of the Lepadidæ is likewise thus formed. The peduncle being filled by the branching ovarian tubes is no objection to this view, for I am informed on the high authority of Mr. J. D. Dana,[12] that this is the case with the cephalo-thorax in some true Crustaceans, for instance, in Sapphirina. To proceed, the mouth, formed of mandibles, maxillæ, and outer maxillæ, correspond with the fourth, fifth, and sixth segments of the archetype Crustacean. Posteriorly to the mouth, we come, in the larva, to a rather wide interspace without any apparent articulation or organ, and then to the thorax, formed of six segments, bearing the six pair of limbs, of which the first pair differs slightly from the others. The thorax is succeeded by three small segments, differently shaped, with the posterior one alone bearing appendages; these segments, I cannot doubt, from their appearance alone, and from their apparent function of steering the body, are abdominal segments. If this latter view be correct, the thoracic segments are the six posterior ones of the normal seven segments, and there must be two segments missing between the outer maxillæ and first thoracic pair of legs, which latter on this view springs from the ninth segment. Now, in a very singular Cirripede, already alluded to under the name of Proteolepas, the two missing segments are present, the mouth being actually succeeded by eight segments, and these by the three usual abdominal segments,—every segment in the body being as distinct as in an Annelid: hence in Proteolepas, adding the three segments for the mouth and three for the carapace, we have altogether seventeen segments, which, as I stated, is the full number ever observed in any Cirripede, the four missing ones being abdominal, and, I presume, the four terminal segments. That the cavity in which the thorax is lodged, in the larva and therefore in the mature Cirripede, is simply formed by the backward production of the carapace, does not require any discussion. The valves have no homological signification.

[12] This distinguished naturalist has given his opinion in the 'American Journal of Science,' March, 1846, that "the pedicel of Anatifa corresponds to a pair of antennæ in the young;" although the peduncle or pedicel is undoubtedly thus terminated, even in mature individuals, I think it has been shown that it is the whole of the anterior part of the larva in front of the mouth, which is directly converted into the peduncle. Professor E. Forbes, in his Lectures, and Professor Steenstrup, in his 'Untersuchungen über das vorkommen des Hermaphroditismus in der Natur,' ch. v, have considered the peduncle as a pair of fused legs. Lovén has taken, judging from a single sentence, the same view of the homologies of the external parts as I have done; in his description of Alepas squalicola, (Ofversigt of Kongl. Vetens., &c., Stockholm, 1844, pp. 192-4), he uses the following words: "Capitis reliquæ partes, ut in Lepadibus semper, in pedunculum mutatæ et

involucrum

," &c.; his involucrum is the same as the capitulum of this work.

As we have just seen that the first pair of natatory legs is borne on the ninth segment of the body, so it must be with the first pair of cirri, which consequently correspond to the outer maxillipods (the two inner pair of maxillipods or pied-machoires being here aborted) of the higher Crustacea, and hence their difference from the five posterior pair, which correspond with the five, ordinary pair of ambulatory legs in these same Crustacea. The part of the body, which I have called the prosoma, that is the protuberant, non-articulated, lower part of the thorax (Pl. IX, fig. 4 n), is a special development, either of the ninth segment, bearing the first pair of cirri, or of the segments corresponding with the organs of the mouth. The three abdominal segments of the larva are represented in the mature Cirripede, in the Order containing the Lepadidæ, only by a minute, triangular gusset, let in between the V-shaped tergal arches of the last thoracic segment: in this gusset, small as it is, is seated the anus, and on each side the caudal appendages, often rudimentary and sometimes absent. In another order, I may remark, (including, probably, the Alcippe of Mr. Hancock,) the cirri, of which there are only three pair, are abdominal.

I feel much confidence, that the homologies here given are correct. The cause of their having been generally overlooked arises, I believe, from the peculiar manner, already described, in which the animal, during its last metamorphosis, is internally almost intersected: even for some little time after discovering that the larval antennæ were always embedded in the centre of the surface of attachment, I did not perceive, that this was the anterior end of the whole animal. The accompanying woodcut gives at a glance, a view of the homologies of the external parts: the upper figure (from Milne Edwards) is a Stomapod Crustacean, Leucifer of Vaughan Thompson, and the abdomen, which we know becomes in Cirripedes, after the metamorphosis, rudimentary, and therefore does not fairly enter into the comparison, is given only in faint lines: the lower figure is a mature Lepas, with the antennæ and eyes, which are actually present in the larva, retained and supposed to have gone on growing. All that we externally see of a Cirripede, whether pedunculated or sessile, is the three anterior segments of the head of a Crustacean, with its anterior end permanently cemented to a surface of attachment, and with its posterior end projecting vertically from it.

[m.—Mouth.]

CAPITULUM.

I will now proceed to a general description of the different parts and organs in the Lepadidæ. The Capitulum is usually much flattened, but sometimes broadly oval in section. It is generally formed of five or more valves, connected together by very narrow or broad strips of membrane; sometimes the valves are rudimental or absent, when the whole consists of membrane. When the valves are numerous, and they occasionally exceed a hundred in number, they are arranged in whorls, with each valve generally so placed as to cover the interval between the two valves above. Of all the valves, the scuta are the most persistent; then come the terga, and then the carina; the rostrum and latera occur only in Scalpellum and Pollicipes, and in a rudimentary condition in Lithotrya, and, perhaps, in the fossil genus Loricula. The valves are formed sometimes of chitine (as in Ibla and Alepas), but usually of shell, which varies from transparency to entire opacity. The shell is generally white, occasionally reddish or purple; exteriorly, the valves are covered by more or less persistent, generally yellow, strong membrane. The scuta and terga are always considerably larger than the other valves: in the different genera the valves differ so much in shape that little can be predicated of them in common; even the direction of their lines of growth differs,—thus, in Lepas and some allied genera, the chief growth of the scuta and of the carina is upwards, whereas in Pollicipes and Lithotrya, it is entirely downwards; in Oxynaspis, and some species of Scalpellum, it is both upwards and downwards. Even in the same species, there is often very considerable variation in the exact shape of the valves, more especially of the terga. The adductor muscle is always attached to a point not far from the middle of the scuta, and it generally has a pit for its attachment. In several genera, namely, Pæcilasma, Dichelaspis, Conchoderma, and Alepas, the scuta show a tendency to be bilobed or trilobed. The valves are placed either at some distance from each other, or close together; but their growing margins very rarely overlap each other, though this is sometimes the case with their upper, free, tile-like apices; in a few species the scuta and terga are articulated together, or united by a fold. The membrane connecting the valves, where they do not touch each other, is like that forming the peduncle, and is sometimes brilliantly coloured crimson-red; generally, it appears blueish-gray, from the corium being seen through. Small pointed spines, connected with the underlying corium by tubuli, are not unfrequently articulated on this membrane: the tubuli, however, are often present where there are no spines. To allow of the growth of the capitulum, the membrane between the valves splits at each period of exuviation, when a new strip of membrane is formed beneath, connected on each side with a fresh layer of shell,—the old and outer slips of membrane disintegrating and disappearing: when there are many valves, the line of splitting is singularly complicated. This membrane consists of chitine,[13] and is composed of numerous fine laminæ. After the valves have been placed in acid, a residue, very different in bulk in different genera, is left, also composed of successive laminæ of chitine. It appears to me that each single lamina of calcified chitine, composing the shell, must once have been continuous with a non-calcified lamina in the membrane connecting the several valves: at the line where this change in calcification supervenes, the chitine generally assumes some colour, and becomes much harder and more persistent; and as the whole valve is formed of component laminæ thus edged (the once continuous laminæ of non-calcified chitine connecting the valves, having disintegrated and disappeared) the surfaces of the valves are generally left covered by a persistent membrane, constituted of these edgings: this membrane has been called the epidermis. In some genera, as in Lepas, this so-called epidermis is seldom preserved, excepting on the last zone of growth: in Scalpellum and Pollicipes it usually covers the whole valves. It appears to me that the laminæ of chitine, and of calcified chitine composing the valves, are both formed not by secretion, but by the metamorphosis of an outer layer of corium into these substances.

[13] Chitine is confined to the Articulata. It was Dr. C. Schmidt (Contributions, &c., being a Physiologico-Chemical investigation: in Taylor's 'Scientific Memoirs,' vol. v), who discovered that the membrane connecting the valves and forming the peduncle, and the tissues of the internal animal, were composed of this substance. But Dr. Schmidt says that the valves in Lepas are composed of 3.09 of albuminates, and 96.81 of incombustible residue; I cannot but think that the existence of the albuminates is an error caused by Dr. Schmidt's belief that the Cirripedia were intermediate between Crustacea and Mollusca, in the shells of which latter, the animal basis consists of albuminates. For after placing the valves of Lepas and Pollicipes in cold acid, I found that the membrane left could not be dissolved in boiling caustic potash, but could, though slowly, (and without change of colour,) in boiling muriatic acid; and these are the main diagnostic characters of Chitine, compared with albuminous substances. I may add, that Schmidt was also induced to consider the shells of Cirripedia as having the same nature with those of Mollusca, from finding that in the above 96.81 of incombustible matter, 99.3 consisted of carbonate and only 0.7 of phosphate of lime; but Dr. Schmidt's own analyses prove how extremely variable the proportions of these salts are in the Crustacea, as the following instance shows:—

 

Lobster.

Squilla.

Phosphate of Lime

12.06

47.52

Carbonate of Lime

87.94

52.48

And, therefore, it is not very surprising that Cirripedia should have still less phosphate of lime in their shells, than has a lobster compared with a squilla.

Within the capitulum is the sack, which, together with the upper internal part of the peduncle, encloses the animal's body. The sack is lined by a most delicate membrane of chitine, under which there is a double layer of corium; this double layer is united together by short, strong, transverse bundles of fibres, branched at both ends:[14] in some genera, the ovarian tubes extend between these two layers. We have seen, under the head of the Metamorphoses, that the delicate tunic lining the sack is simply a duplicature of the thick membrane and valves forming the capitulum, the whole being the posterior portion of the carapace of the larva slightly modified.

[14] I am much indebted to Mr. Inman of Liverpool for having kindly sent me excellent specimens illustrating this structure.

Peduncle.—Its length varies greatly in different species, and even in the same species, according to the situation occupied by the individual; its lower end is sometimes pointed, but generally only a little narrower than the upper end. In outline, the peduncle is usually flattened, but sometimes quite cylindrical. It is composed of very strong, generally thick, transparent membrane, rarely coloured reddish, and often penetrated by numerous tubuli. The underlying corium is sometimes coloured in longitudinal bands. At each period of growth a new and larger integument is formed under the old one, which gradually disintegrates and disappears; the extreme lower point is often deserted by the corium, and ceases to grow, whilst the whole upper part still continues increasing in diameter: in length the chief addition is made (as is clearly seen in those genera having calcified scales), round the upper margin, at the base of the capitulum. The surface of the membrane is either naked or superficially clothed with minute, pointed, articulated spines, or it is penetrated by calcified scales or styles, (in Ibla alone formed of chitine,) which pass through it to the corium, and are added to at their bases, like the valves, at each period of growth. In Lithotrya alone the scales of the peduncle are moulted together with the connecting membrane. These scales on the peduncle are generally placed symmetrically in whorls, with each scale corresponding with the junctions of two scales, both above and below. Except in Scalpellum ornatum and the fossil Loricula pulchella, they are very small compared with the valves of the capitulum. When the scales are symmetrical, new ones are first formed only round the summit of the peduncle, and only those in the few uppermost whorls continue to grow or to be added to at their bases; afterwards membrane is deposited under them. The shelly matter of the scales resembles that of the valves, and the manner of growth is the same; tubuli generally run to and through them from the corium. From the continued enlargement of the membrane of the peduncle, the scales come to stand, in the lower portion, some way apart. In Ibla, new horny styles are formed indifferently in all parts of the peduncle. In some species of Pollicipes, the calcareous styles are not symmetrical or symmetrically arranged; and besides those first formed round the top of the peduncle, there are other and larger ones formed near its base. Lastly, in Lithotrya we have a row of calcareous discs or an irregular, basal cup, formed in the same manner as the valves of the capitulum: in this genus alone (as already stated,) the calcified scales are moulted, and here alone their edges are serrated.

The peduncle is lined within by three layers of muscles, longitudinal, transverse, and oblique, all destitute of the transverse striæ, characteristic of voluntary muscles; they run from the bottom of the peduncle to the base of the capitulum, as in Lepas, or half way up it, as in Conchoderma; in Alepas alone they surround the whole capitulum up to its summit. In Lithotrya there are two little, fan-like, transverse muscles (involuntary), extending from the basal points of the terga to a central line on the under side of the carina. The gentle swaying to and fro movements, and the great power of longitudinal contraction,—movements apparently common, as I infer from facts communicated to me by Mr. Peach, to all the Pedunculata,—are produced by these muscles. The interior of the peduncle is filled up with a great mass of branching ovarian tubes; but in Ibla and Lithotrya, the upper part of the peduncle is occupied by the animal's body.

Means of Attachment.—If the peduncle be very carefully removed (Tab. IX, fig. 7 and Tab. I, fig. 6 b), from the surface of attachment, quite close to the end, but not at the actual apex, the larval prehensile antennæ can always be found: these have been sufficiently described for our present purpose under the head of the Metamorphoses; but I may add, that the diagnostic differences between them in the several genera are briefly given, for a special purpose, in a discussion on the sexes of Scalpellum at the end of that genus. We have seen in the larva, that the cement-ducts, with their opaque cellular contents, can be traced from within the discs of the antennæ to the anterior or lower ends of the two gut-formed bodies, which it can be demonstrated are the incipient ovaria.

In mature Cirripedes these ducts can be followed, in a slightly sinuous course, along the muscles on each side within the peduncle, till they expand into two small organs, which I have called cement-glands. These glands are found with great difficulty, except in Conchoderma aurita, where they are placed on each side under the inner layer of corium, at the bottom of the sack, so as to be just above the top of the peduncle; they resemble in shape a retort, (Pl. IX, fig. 3.). In Pollicipes mitella and polymerus they lie half way down the peduncle, close together, and apparently enclosed within a common membrane; in these two species the broad end of the gland is bent towards the neck of the retort. In Scalpellum the position is the same, but the shape is more globular. In Ibla the structure is more simple, namely, a tube slightly enlarged, running downwards, bent a little upwards, and then resuming its former downward course, the lower portion forming the duct. The gland contains a strongly coherent, pulpy, opaque, cellular mass, like that in the cement-ducts; but in some instances, presently to be mentioned, this cellular mass becomes converted within either the ducts or gland, or within both, into transparent, yellow, tough cement. Generally in Conchoderma, Pollicipes, and Scalpellum, two ovarian tubes, but in one specimen of Conchoderma aurita, three tubes, and in Ibla one tube could be seen running into or forming the gland; of the nature of the tubes there could not be the least doubt, for at a little distance from the glands they gave out branches (Pl. IX, fig. 3), containing ova in every state of development. In some specimens as in that figured of Conchoderma aurita, the ovarian tube on one side of the gland is larger than on the other, and has rather the appearance of being deeply embedded in the gland than of forming it; but, in other specimens, the two ovarian tubes first formed a little pouch, into which their cellular contents could be clearly seen to enter; and then this pouch expanded into the gland; thus quite removing a doubt which I had sometimes felt, whether the ovarian tube was not simply attached to or embedded in the gland, without any further connection. By dissection the multiple external coats of the gland and ovarian tubes could be seen to be continuous. The cellular contents of the tubes passed into the more opaque cellular contents of the gland, by a layer of transparent, pulpy, pale, yellowish substance. There appeared in several instances to be a relation, between the state of fulness and condition of the contents of the gland, and of the immediately adjoining portions of the ovarian tubes. In one specimen of Pollicipes mitella it was clear that the altered, tough, yellow, transparent, non-cellular contents of the two glands and ducts, had actually invaded for some little distance, the two ovarian tubes which ran into them, thus showing the continuity of the whole. From these facts I conclude, without hesitation, that the gland itself is a part of an ovarian tube specially modified; and further, that the cellular matter, which in the ovarian tubes serves for the development of the ova, is, by the special action of the walls of the gland, changed into the opaquer cellular matter in the ducts, and this again subsequently into that tissue or substance, which cements the Cirripede to its surface of attachment.

As the individuals grow and increase in size, so do the glands and cement-ducts; but it seems often to happen, that when a specimen is immovably attached, the cementing apparatus ceases to act, and the cellular contents of the duct become converted into a thread of transparent tough cement; the investing membrane, also, of the ducts, in Conchoderma sometimes becomes hard and mamillated. I have already alluded to the case of a Pollicipes, in which both glands and ducts, and even a small portion of the two adjoining ovarian tubes, had become thus filled up. As in sessile Cirripedes, at every fresh period of growth a new cement gland is formed, it has occurred to me, that possibly in Pollicipes something similar may take place. In sessile Cirripedes, the old cement-glands are all preserved in a functionless condition, adhering to the membranous or calcareous basis, each new larger one attached to that last formed, and each giving out cement-ducts, which, bifurcating in the most complicated manner, pass outside the shell and thus attach it to some foreign body.

The cement, removed from the outside of a Cirripede, consists of a thin layer of very tough, bright-brown, transparent, laminated substance, exhibiting no structure under the highest powers, or at most a very fine dotted appearance, like a mezzotinto drawing. It is of the nature of chitine; but boiling caustic potash has rather more effect on it than on true chitine; and I think boiling nitric acid rather less effect. In one single instance, namely, in Coronula, the cement comes out of the four orifices of the two bifurcating ducts, in the shape of distinct cells, which, between the whale's skin and the basal membrane, arrange themselves so as to make a circular, continuous slip of cement; then the cells blend together, and are converted into transparent, structureless cement. Cementing tissue or membrane would, perhaps, have been a more correct title than cement; but, in ordinary cases, its appearance is so little like that of an organised tissue, that I have for this reason, and for brevity-sake, preferred the simple term of Cement.

In the larva the cement always escapes through the prehensile antennæ; and it thus continues to do throughout life in most or all of the species of Lepas, Conchoderma, Dichelaspis and Ibla. In the first two of these genera, the cement escapes from the borders of the lower side of the disc or penultimate segment of the antennæ, and can be there seen radiating out like spokes, which at their ends divide into finer and finer branches, till a uniform sheet of cement is formed, fastening the antennæ and the adjoining part of the peduncle down to the surface of attachment. In Dichelaspis Warwickii and Scalpellum Peronii, the cement, or part at least, comes out of the ultimate segment of the antennæ, in the shape of one tube, within another tube of considerable diameter and length. In Scalpellum vulgare, and probably in some of the other species, which live attached to corallines, the cement soon ceases to debouch from the antennæ, but instead, bursts through a row of orifices on the rostral margin of the peduncle (Pl. IX, fig. 7), by which means this margin is symmetrically fastened down to the delicate, horny branches of the zoophyte. In Pollicipes, the two cement-ducts, either together or separately (Pl. IX, fig. 2, 2 a´), wind about the bottom of the peduncle in the most tortuous course, at each bend pouring out cement through a hole in the membrane of the peduncle. In Ibla the lower part of the peduncle is internally filled by cement, and thus rendered rigid. In Lepas fascicularis a vesicular ball of cement surrounding the peduncle is thus formed (Pl. I, fig. 6), and serves as a float! All these curious, special adaptations are described under the respective genera. How the cement forces its way through the antennæ, and often through apertures in the thick membrane of the peduncle, I do not understand. I do not believe, though some appearances favoured the notion, that the duct itself debouches and divides, at least this is not the case in Coronula, but only that the internal chord of cellular matter thus acts and spreads itself out; nor do I understand how, when the antennæ and immediately adjoining parts are once cemented down, any more cement can escape; yet this must take place, as may be inferred from the breadth of the cemented, terminal portion of the peduncle in Lepas and Conchoderma; and from the often active condition in old individuals of the cementing organs.

I have entered on this subject at some length, (and I wish I had space for more illustrations,) from its offering, perhaps, the most curious point in the natural history of the Cirripedia. It is the one chief character of the Sub-class. I am well aware how extremely improbable it must appear, that part of an ovarian tube should be converted into a gland, in which cellular matter is modified, so that instead of aiding in the development of new beings, it forms itself into a tissue or substance, which leaves the body[15] in order to fasten it to a foreign support. But on no other view can the structure, clearly seen by me both in the mature Cirripede and in the larva, be explained, and I feel no hesitation in advancing it. I may here venture to quote the substance of a remark made by Professor Owen, when I communicated to him the foregoing facts, namely, that there was a new problem to solve,—new work to perform,—to attach permanently a crustacean to a foreign body; and that hence no one could, a priori, tell by what singular and novel means this would be effected.

[15] The protrusion of the egg-bearing pouches in Cyclops and its kindred genera, outside the body, offers a feeble analogy with what takes place in Cirripedes. Professor Allman ('Annals of Natural History,' vol. xx, p. 7,) who has attended to the subject, says that the external egg-bearing pouches are "a portion of the membrane of the true ovaries:" if the membrane of these pouches had been specially made adhesive, the analogy would have been closer.

Filamentary Appendages.—These have generally been considered to act as branchiæ; they occur at the bases of the first pair of cirri in Lepas, Alepas, Conchoderma, and in three species of Pollicipes: in Conchoderma there are similar appendages attached to the pedicels of the cirri (Pl. IX, fig. 4, g-k); and in the above three species of Pollicipes there is a double row of them on the prosoma: their numbers differ in different species (in some there being none) of the same genus, and even in different individuals of the same species; they are entirely absent in the majority of the genera. These facts would indicate that they are not of high functional importance; and they seem so generally occupied by testes (Pl. iv, fig. 5), that I suspect their function is quite as much to give room for the development of these glands, as to serve for respiratory purposes. With the exception of the four above-named genera, the mere surface of the body and of the sack must be sufficient for respiration: in Conchoderma aurita the two great expansions of surface, afforded by the folded, tubular, ear-like projections, aid, as I believe, towards this end.

The shape of the body varies, owing to the greater or less development of the lower part of the prosoma, the greater or less distance of the first from the second pair of cirri, and of the mouth from the adductor scutorum muscle, (Pl. IX, fig. 4, and Pl. IV, 8 a´). In all the genera, the body is much flattened. I may here mention a few particulars about the muscular system. One of the largest muscular masses is formed by the adductor scutorum, and by the muscles which surround in a double layer (the fasciæ being oblique to each other) the whole of the upper part of the prosoma. From under the adductor, a pair of delicate muscles runs to the basal edge of the labrum, so as to retract the whole mouth, and two other pair to the integument between the mouth and the adductor, so as to fold it: again, there are other delicate muscles in some (for instance in Lepas Hillii) if not in all the Lepadidæ, crossing each other in the most singular loops, and serving apparently to fold the membrane between the occludent edges of the scuta. Within the prosoma there is a strong adductor muscle, running straight from side to side, for the purpose, as it appears, of flattening the body. The thorax, on the dorsal and ventral surfaces, is well furnished with straight and oblique muscles (without striæ), which straighten and curl up this part of the body. The muscles running into the pedicels of the cirri, cross each other on the ventral surface of the thorax; the muscles within the rami are attached to the upper segments of the pedicels. Finally, I may remark that the whole of the body and the cirri are capable of many diversified movements.

Mouth.—This is prominent, and almost probosciformed (Pl. IX, fig. 4 b), and in the abnormal Anelasma (Pl. IV, fig. 2 d), quite probosciformed,—such, also, was its character in the larval condition. In outline, it is either sub-triangular, or oval with the longer axis transverse; the whole is capable, as well as the separate organs, of considerable movement, as I have seen in living sessile Cirripedes. It is composed (Tab. V, fig. 2) of a labrum, swollen or bullate, often to such an extent as to equal in its longitudinal axis the rest of the mouth; of palpi soldered to the labrum; of mandibles, maxillæ, and outer maxillæ, the latter serving as a lower lip. These organs have only their upper segments free, but there are traces, clearly seen in the mandibles (Pl. X, fig. 1, a, b), of their being formed of three segments. The two lower segments are laterally united, and open into each other, the prominence of the mouth being thus caused: this condition appears to me curious, and is, to a certain limited extent, intermediate between those articulated animals which have their trophi soldered into a proboscis, and those furnished with entirely free masticatory or prehensile organs. The palpi adhere to the corners of the labrum; and I call them palpi only from seeing that they spring laterally from above the upper articulation of the mandibles. The prominence of the mouth, measured from the basal fold by which the whole is separated from the body, is much greater on the half formed by the labrum and mandibles, than on the other half facing the cirri. The trophi surround a cavity—the supra-œsophageal cavity—in the middle of which, between the mandibles is seated the orifice of the œsophagus. The œsophagus is surrounded by long, fine, muscular fasciæ, radiating in all directions, opposing the constrictor muscles, and is capable of violent swallowing movements,—constriction after constriction being seen to run down its whole course: there are also some fine muscles attached to the membrane forming the supra-œsophageal cavity. The trophi serve merely for the prehension of prey, and not for mastication.

The Labrum, as stated, is always bullate or swollen; and sometimes the upper exterior part forms, as in Ibla (Pl. IV, fig. 8 a, c), and Dichelaspis, an overhanging blunt point. The object, I suspect, of this bullate form is to give, in the upper part, attachment to longer muscles running to the lateral surfaces of the mandibles, and lower down to the œsophagus. The crest close over the supra-œsophageal cavity, is generally furnished with small, often bead-like teeth. The Palpi are small, their apices never actually touching each other; they are more or less blunt, not differing much in shape in the different genera (Pl. X, figs. 6 to 8), and clothed with spines. They are not capable of movement; their function seems to be to prevent prey, brought by the cirri, escaping over the labrum; I infer this from finding in Anelasma and in the male of Ibla, which have the cirri functionless, that the palpi are rudimentary.

The Mandibles (Pl. X, figs. 1-5) have from two to ten strong teeth in a single row; where the number exceeds five, several of the teeth are small; the inferior angle is generally pectinated with fine spines; in Lithotrya (fig. 2), the interspaces between the teeth are also pectinated. In the same individual there is not unfrequently one tooth, more or less, on opposite sides of the mouth. Internally, the mandibles are furnished on their outer and inner sides with several ligamentous apodemes, in Lithotrya roughened with points (Pl. X, fig. 2), for the attachment of the muscles; of these (fig. 1), there is a chief depressor and elevator, attached at their lower ends to near the basal fold of the mouth, and a lateral muscle, attached to the broad basal end of the palpi, and serving, apparently, to oppose the edge of mandible to mandible. The Maxillæ in the different genera (Pl. X, figs. 9 to 15) differ considerably in outline; they are generally about half the size of the mandibles; at the upper corner, there are always two or three spines larger than the others, and often separated from them by a notch; the rest of the spinose edge is straight, or irregular, or step-formed, or with the lowest part projecting, or with one or two narrow prominences bearing fine spines. All these spines, quite differently from the teeth of the mandibles, are articulated on the edge of the organ, and stand in a double row. At a point corresponding with the upper articulation of the mandibles, a long, thin, narrow, rigid apodeme, projects inwards (fig. 10), and running down nearly parallel to the thin, outer, flexible membrane of the mouth, is attached to the corium, and thus serves as a support to the whole organ. This apodeme is embedded in muscles (Pl. X, fig. 10); there are other large muscles attached to the inner side of the organ, and again others running laterally towards the mandibles. The apodeme, of course, is moulted with the integuments of the mouth. The Outer Maxillæ (Pl. X, figs. 16, 17) serve as a lower lip; they are thicker than the other trophi; they have their inner surfaces clothed with spines, sometimes divided into an upper and lower group, and occasionally separated by a deep notch: there are often long bristles outside. They are furnished with at least two muscles; in sessile Cirripedes I have seen that they are capable of a rapid to and fro movement, and I have no doubt that their function is to brush any small creature, caught by the cirri, towards the maxillæ, which are well adapted to aid in securing the prey, and to hand it over to the mandibles, by them to be forced down the œsophagus. On the exterior face of the outer maxillæ, above a trace of an upper articulation, either two small orifices or two large tubular projections can always be discovered; and these, as will presently be mentioned, I believe to be olfactory organs.

Cirri.—The five posterior pair are seated close to each other and equidistant; the first pair is generally seated at a little distance, and sometimes at a considerable distance from the second pair. The first pair is the shortest; the others, proceeding backwards, increase gradually in length. The rami of each pair are either equal in length or slightly unequal: those of the first pair are oftenest unequal. The number of segments in the posterior cirri is sometimes very great; in one species of Alepas, there were above sixty segments in one ramus, the other ramus being in this unique case (Pl. X, fig. 28) small and rudimentary. The pedicels consist of two segments, a lower, longer, and upper short one (fig. 18, c, d.) In the usual arrangement of the spines on the segments of the three posterior pair of cirri, there are (figs. 26, 27) from three to six pair of long spines on the anterior face, with generally some minute spines (occasionally forming a tuft) intermediate between them: on the dorsal surface, in the uppermost part of each segment, there is a tuft of short spines generally mingled with some longer, finer ones: on the inner side of each segment, on the upper rim, there are generally a few extremely minute and short spines. From the increase of these latter and of the intermediate spines, the antero-lateral faces of the segments of the first cirrus, and of the lower segments of the anterior ramus of the second cirrus (Pl. X, fig. 25), are almost always thickly paved with brush-like masses of spines. The lower segments of the anterior ramus of the third cirrus is generally, though not always, thus paved: these paved segments are much broader than the others. The posterior rami of the second and third cirri are often in some slight degree paved, though in other cases they resemble the three posterior pair of cirri. The two segments of the pedicels have bristles on their anterior faces, essentially arranged on the same plan as on the segments of the rami: the bristles are generally not so symmetrically arranged on the pedicels of the second and third cirri, as on the three posterior pair. There are some exceptions to the foregoing general rules: in the posterior cirri of Alepas cornuta, there is only one pair of long spines to each segment (fig. 28); in Dichelaspis Lowei, there are eight pair; in Lepas fascicularis, in old specimens, the segments are paved with a triangular brush of spines; the upper segments in Pæcilasma eburnea support small oblong brushes; and, lastly, in Pæcilasma fissa (fig. 29), and crassa, the spines form a single circle round each segment, interrupted on the two sides. These spines are often doubly serrated or plumose: many of them on the protuberant segments of the first three pair of cirri, are sometimes coarsely and doubly pectinated.

Caudal Appendages.—These are present (Pl. X, figs. 18 to 24) seated on each side of the anus, in all the genera, except in Conchoderma, Anelasma, and Scalpellum villosum; they consist of a very small single segment, destitute of spines in Lepas, and spinose in Pæcilasma, Dichelaspis, Oxynaspis, Scalpellum, and some species of Pollicipes; they consist of several segments in Alepas, Ibla, Lithotrya, and in some species of Pollicipes. In the latter genus, some species have their caudal appendages multiarticulate, though so obscurely articulated, that the passage (fig. 22) from several to one segment is seen to be easily effected. When the appendage consists of many articulations, it is generally about as long as the pedicel of the sixth cirrus; but in Ibla quadrivalvis, it is four times as long. The segments are narrow, slightly flattened, much tapering; each (fig. 24) is surmounted by a ring of short spines, which are generally longest on the apex of the terminal segment. I could never trace muscles into these appendages.

Alimentary Canal.—The œsophagus is of considerable length: it is formed of strong, transparent, much folded membrane, continuous with the outer integuments, and moulted with them: it is surrounded by corium, and as already stated, by numerous muscles: at its lower end it expands into a bell, with the edges reflexed, and sometimes sinuous: this bell lies within the stomach, and keeps the upper broad end expanded. According to the less or greater distance of the mouth from the adductor muscle, the œsophagus runs in a more or less parallel course to the abdominal surface between the first and succeeding pairs of cirri, and enters the stomach more or less obliquely. In Ibla alone, it passes exteriorly to, and over the adductor scutorum muscle. The stomach lies in a much curved, almost doubled course; it is often a little constricted where most bent; it is broadest at the upper end, and here, in Lepas and Conchoderma, there are some deep branching cæca; in the latter of these two genera, the whole surface is, in addition, pitted in transverse lines. The stomach is coated by small, opaque, pulpy, slightly arborescent glands, believed to be hepatic; these are arranged in longitudinal lines, in all the genera, except in Alepas, in which they are transverse and reticulated: the whole stomach is thus coated. There is, also, a coating of excessively delicate, longitudinal and transverse muscles without striæ. The rectum varies in length, extending inwards from the anus to between the bases of the second and fifth pair of cirri: it is narrow, and formed of much folded transparent membrane, resembling the œsophagus, continuous with the outer integuments, with which it is periodically moulted. The anus is a small longitudinal slit, in the triangular piece of membrane representing the abdomen, let in between the last thoracic tergal arches, as already mentioned under the head of the Metamorphoses; it lies almost between the caudal appendages, and opens on the dorsal surface. Within the stomach, there can generally be plainly seen, in accordance with the period of digestion when the specimen was taken, a thin, yet strong, perfectly transparent epithelial membrane, not exhibiting under the highest power of the microscope any structure: it enters the branching cæca, and extends from the edge of the bell of the œsophagus to the commencement of the closed rectum, and consequently terminates in a point: it consists of chitine, like the outer integuments of the animal, and by placing the whole body in caustic potash, I have dissolved the outer coats of the stomach, and seen the bag open at its upper end, perfectly preserved, floating in the middle of the body, and full of the debris of the food. In most of the specimens which I have examined, preserved in spirits of wine, this epithelial lining was some little way distant and separate from the coats of the stomach; and hence was thought by M. Martin St. Ange to be a distinct organ, like the closed tube in certain Annelids. Occasionally, I have seen one imperfect epithelial bag or tube within another and later-formed one. Digestion seems to go on at the same rate throughout the whole length of the stomach; if there be any difference, the least digested portions lie in the lower and narrower part. The prey, consisting generally of crustacea, infusoria, minute spiral univalves, and often of the larvæ of Cirripedes, is not triturated: when the nutritious juices have been absorbed, the rejectamenta are cast out through the anus, all kept together in the epithelial bag, which is excluded like a model of the whole stomach, with the exception of that part coated by the bell of the œsophagus. I have sometimes thought that the bag was formed so strong, for the sake of thus carrying out the excrement entire, so as not to befoul the sack. I believe Lepas can throw up food by its œsophagus; at least, I found in one case, many half-digested small Crustaceans in the sack, and others of the same kind in the stomach.

Circulatory System.—I can add hardly anything to what little has been given by M. Martin St. Ange: like others, I have failed, as yet, in discovering a heart. The whole body is permeated by channels, which have not any proper coat: there is one main channel along the ventral surface of the thorax, dividing and surrounding the mouth, and giving out branches which enter the inner of the two channels in each cirrus: as Burmeister has shown, there are also two channels in the penis. There are two dorso-lateral channels in the prosoma, which are in direct connection with the great main channel, running down the rostral (i. e., ventral) side of the peduncle. This latter main channel branches out in the lower part, and transmits the fluid through the ovarian tubes, whence, I believe, it flows upwards and round the sack, re-entering the body near the sides of the adductor scutorum muscle. The main rostral channel (or artery?) in the uppermost part of the peduncle, has a depending curtain, which, I think, must act as a valve, so as to prevent the circulating fluid regurgitating into the animal's body during the contractions of the peduncle.

Nervous System and Organs of Sense.—In most of the genera, there are six main ganglia, namely, the supra-œsophageal, and five thoracic ganglia; but in Pollicipes mitella there are only four thoracic ganglia. Of these, the first thoracic or infra-œsophageal ganglion is considerably the largest and most massive; it is squarish, or oval, or heart-shaped; it presents no trace of being formed by the union of two lateral ganglia. Two great nerves spring from its under side (A), represented in the woodcut on page 49, by dotted lines, and run straight down amongst the viscera in the prosoma: these nerves are about as large as those forming the collar and those running to the second ganglion; hence, six great nerves meet here, two in front, two behind, and two on the under side. At the anterior end, over the junction with the collar chord, three equal-sized nerves rise on each side, with a fourth, smaller one, outside; these go to the trophi and to the two olfactory sacks. At the posterior end, on each side, a pair of nerves branch out rectangularly, one of which (a,) goes to the first cirrus, and there divides into two branches; of these, the upper runs up the cirrus, and the lower one downwards. The other nerve (b), proceeding on each side from this first thoracic ganglion, runs to the muscles beneath the basal articulation of the first cirrus. The collar surrounding the œsophagus is generally very long, sometimes equalling the whole thoracic chord; at a middle point, a small branch is sent off, and at the anterior end (e, e), close to the supra-œsophageal ganglia, double or treble fine branches run to the true ovaria, lying close to the upper end of the stomach. The four (or only three) other thoracic ganglia, when viewed as transparent bodies, are seen to be solid; but in some of the genera, as in Conchoderma, the outline plainly shows, that each consists of a lateral pair fused together. The second thoracic ganglion (B) is rather small; it is either close to the first, as in Pollicipes mitella and Lepas fascicularis, or far distant, as in Ibla. The third (C) and fourth are of about the same size with the second: these three ganglia send large branches to the second, third, and fourth pair of cirri: other minute branches spring from their under sides, and from the intermediate double chords. The fifth ganglion is larger and longer than the three preceding ones, and gives off nerves to the fifth and sixth pair of cirri; it is clearly formed by the union of the fifth, with what ought to have formed a sixth ganglion. The two nerves going to the sixth cirrus give off on their inner sides, each a great branch to the penis. In Pollicipes mitella, in which there are only four instead of five thoracic ganglia, it is evident from the outline and position of the nerves going to the fourth pair of cirri, that the fourth ganglion is fused into the fifth, itself, as we have just seen, normally composed of two consecutive ganglia. In this Pollicipes there is other evidence of concentration in the nervous system, for none of the ganglia show signs of being formed of lateral pairs; the second is close to the first; and the abdominal double chord is in part separated by a mere cleft; lastly, as we shall immediately see, the same remark is applicable to the supra-œsophageal ganglia.

The latter (D) alone remain to be described; they present far more diversity in shape than do the thoracic ganglia; they are almost always seen in outline to be laterally distinct, and usually resemble two pears with their tapering ends cut off and united; in a transverse line they are as long as the infra-œsophageal ganglion, but are much less massive. In Lepas fascicularis (D), they are pear-shaped; in Pollicipes mitella they are globular, and separated by a third globular ganglion, which I believe is the ophthalmic ganglion, presently to be described; in Pollicipes spinosus, however, the ophthalmic ganglion is, as usual, placed in advance of the supra-œsophageal ganglion, which latter, in this one species, shows no sign of being formed of a lateral pair fused together. In Alepas cornuta the supra-œsophageal ganglion consists of two quite distinct ganglia, elongated in the longitudinal axis of the body, and separated from each other by the whole width of the mouth; the chord which unites them is of the same thickness as the rest of the collar. In all the genera, from the front of each of the two supra-œsophageal ganglia, a pair of nerves, (f, f,) united and together as large as the collar nerve, rises, and can be traced running unbranched, in a nearly straight line, for a length equalling the whole rest of the nervous chord, so as to supply the peduncle and the inside of the capitulum or sack. At the inner ends of these two same ganglia, from a central point where they are united, a little central branch runs in front to the adductor scutorum and other adjoining muscles; and still smaller fibrils run behind to the œsophageal muscles.

Diagram of the anterior portion of the nervous system in Lepas fascicularis. A. First thoracic or infra-œsophageal ganglion. B. Second thoracic. C. Third thoracic ganglion. D. Supra-œsophageal ganglion. E. The two ophthalmic ganglia. F. Double eye. a. Nerve going to first cirrus; b, to the muscles below the first cirrus; c, to the second cirrus; d, to the third; e, nerves running to the ovaria; f, double nerves supplying the sack and peduncle.

Ophthalmic Ganglia and Eyes.—Owing to Professor Leidy's[16] discovery of eyes in a Balanus, I was led to look for them in the Lepadidæ. Extending from the front of the two supra-œsophageal ganglia, two chords may be seen in Lepas fascicularis (of which a rude diagram is here given), to run into two small, perfectly distinct oval ganglia (E), which are not united by any transverse commissure. From the opposite ends of these two ganglia smaller nerves run, and, bending inwards at right angles, enter, beyond the middle, an elongated (F), almost black, eye, composed of two eyes united together. Although in outline the eye appears single, two lenses can be distinctly seen at the end, directed upwards and towards the ganglia; two pigment-capsules can also be distinguished; these are deep and cup-formed, and of a dark reddish-purple. The following measurements will show the proportions of the parts in a specimen of the Lepas fascicularis having a capitulum 4/10ths of an inch in length.

Double eye

length

26/6000

 

width

13/6000

Diameter of single lens

 

6/6000

Ophthalmic ganglion

length

16/6000

 

breadth

11/6000

Supra-œsophageal ganglion, transverse or longest axis of both together

126/6000

Supra-œsophageal ganglion, longitudinal axis of

45/6000

Infra-œsophageal ganglion, transverse axis of

120/6000

Infra-œsophageal ganglion, longitudinal axis of

114/6000

[16] Proceedings of the Academy of Natural Sciences, Philadelphia. No. i, vol. iv, Jan. 1848.

In Conchoderma aurita the ophthalmic ganglia are much smaller, and nearer to the supra-œsophageal ganglion, than in L. fascicularis. In Alepas cornuta the ophthalmic chords run towards each other from the two distant and separate supra-œsophageal ganglia; and the ophthalmic ganglia, (instead of being quite separate, as in L. fascicularis,) are united by their front ends, and the two eyes instead of standing some way in front, with nerves running to them, are embedded on the double ophthalmic ganglion; the pigment-capsules here, also, have the shape of mere saucers, and are joined back to back, with the two lenses projecting far out of them. In neither sex of Ibla could I perceive that the eye was double. In Pollicipes spinosus the ophthalmic ganglion stands in front of the single supra-œsophageal ganglion, and shows no signs of being formed of a lateral pair; the eyes themselves, however, differently from, in all the foregoing cases, are, though approximate, quite distinct. In Pollicipes mitella I did not see the eyes; but the ophthalmic ganglion consists, as I believe, of a single globular one, placed exactly between the two globular, supra-œsophageal ganglia, all three being of nearly equal size. Professor Leidy does not mention the ophthalmic ganglia; hence I infer that in Balanus, which is a more highly organised Cirripede, they are fused into the supra-œsophageal ganglion.

In all the genera, the double eye is seated deep within the body; it is attached by fibrous tissue to the radiating muscles of the lowest part of the œsophagus, and lies actually on the upper part of the stomach; consequently, a ray of light, to reach the eye, has to pass through the exterior membrane and underlying corium connecting the two scuta, and to penetrate deeply into the body. In living sessile Cirripedes, vision seems confined to the perception of the shadow of an object passing between them and the light; they instantly perceived a hand passed quickly at the distance of several feet between a candle and the basin in which they were placed.

As the infra-œsophageal ganglion sends nerves to the trophi and to the first pair of cirri, it must correspond to the segments, from the fourth to the ninth inclusive, of the archetype crustacean. The state of the supra-œsophageal and ophthalmic ganglia appears to me very interesting: I do not believe that in any mature ordinary crustacean, the first or ophthalmic ganglion can be shown to be distinct from the two succeeding ganglia, or to be itself composed of a pair laterally distinct. The ganglia, corresponding with the second and third segments of the body, which should normally support two pair of antennæ, are in the Lepadidæ united together; but laterally they are generally distinct in outline, and are actually separate in Alepas: the supra-œsophageal ganglion shows also its double nature, by giving rise to a pair of large double nerves, evidently corresponding with the two pair of antennular nerves in ordinary crustaceans. The embryonic condition of the whole supra-œsophageal portion of the nervous system in the Lepadidæ, corresponds with the rudimentary state of the only organ of sense supplied by it, namely, the eye, which in size and general appearance has retrograded to the state in which it was in, during the first stage of development of the larva;—I have used the term embryonic, because, in the embryos of ordinary crustacea, all the ganglia are at first longitudinally distinct, and laterally quite separate. The conclusion at which we before arrived from studying the metamorphoses, namely, that the whole peduncle and capitulum consisted of the first three segments of the head, is beautifully supported by the structure of the nervous system, in which these parts are seen to be supplied with nerves exclusively from the supra-œsophageal ganglion: now in ordinary crustacea the supra-œsophageal ganglion sends nerves to the eyes and the two pair of antennæ corresponding, as is known by embryological dissections, to the first three segments of the body. Moreover, it is asserted that the carapace which covers the thorax in crustacea, is not formed by the development of the first segment; and this, likewise, may be inferred to be the case with the peduncle and capitulum in the Lepadidæ, as the nerves of the ophthalmic ganglia go exclusively to the eyes. Finally, I may remark that in Pollicipes, looking to the whole nervous system, the state of concentration nearly equals that in certain macrourous decapod crustaceans, for instance the Astacus marinus, of which a figure is given by Milne Edwards.

Olfactory Organs.—In the outer maxillæ, at their bases where united together, but above the basal fold separating the mouth from the body, there are, in all the genera, a pair of orifices (Pl. X, fig. 16); these are sometimes seated on a slight prominence, as in Lithotrya, or on the summit of flattened tubes (Pl. X, fig. 17), projecting upwards and towards each other, as in Ibla, Scalpellum, and Pollicipes. In Ibla these tubular projections rise from almost between the outer and inner maxillæ. It is impossible to behold these organs, and doubt that they are of high functional importance to the animal. The orifice leads into a deep sack lined by pulpy corium, and closed at the bottom. The outer integument is inflected inwards, (hence periodically moulted,) and becoming of excessive tenuity, runs to near the bottom of the sack, where it ends in an open tube: so excessively thin is this inflected membrane, that, until examining Anelasma, I was not quite certain that I was right in believing that the outer integument did not extend over the whole bottom. I several times saw a nerve of considerable size entering and blending into a pulpy layer at the bottom of the sack of corium; but I failed in tracing to which of the three pair of nerves, springing from the front end of the infra-œsophageal ganglion, it joined. I can hardly avoid concluding, that this closed sack, with its naked bottom, is an organ of sense; and, considering that the outer maxillæ serve to carry the prey entangled by the cirri towards the maxillæ and mandibles, the position seems so admirably adapted for an olfactory organ, whereby the animal could at once perceive the nature of any floating object thus caught, that I have ventured provisionally to designate the two orifices and sacks as olfactory.

Acoustic (?) Organs.—A little way beneath the basal articulation of the first cirrus (Pl. IX, fig. 4 d, and Pl. IV, fig. 2 e), on each side, there may be seen a slight swelling, and on the under side of this, a transverse slit-like orifice, 1/20th of an inch in length in Conchoderma, but often only half that size. In Ibla this orifice is seated lower down (Pl. IV, fig. 8 a´, e), between the bases of the first and second cirri, which are here far apart: in Alepas cornuta it is placed rather nearer to the adductor scutorum muscle, namely, beneath the mandibles. The orifice leads into a rather deep and wide meatus; the external integument is turned in for a short distance, widening a little, and then ends abruptly. The meatus, enlarging upwards, is lined by thick pulpy corium, and is closed at the upper end; from its summit is suspended a flattened sack of singular and different shapes in the different genera. This, the so-called acoustic sack of Conchoderma virgata, is figured Pl. IX, fig. 6. The deep and wide notch faces towards the posterior end of the animal; the inferior lobe, thus almost cut off, is flattened in a different plane from the upper part; the lobe is lodged in a little pouch of corresponding form, leading from the open meatus in which the upper part is included. In Conchoderma aurita, the top of the acoustic sack is narrower and more constricted, the whole more rounded, and the lobe more turned down. In Lepas fascicularis the notch is not so deep or wide, and the lobe larger. In Ibla Cumingii the sack is of the shape of a vase, with one corner folded over. In Scalpellum vulgare it is small, oval, with the lower end much pushed in, and furnished with a little crest. Lastly, in Pollicipes mitella it is simply oval. In all cases the sack is empty, or contains only a little pulpy matter: it consists of brownish, thick, and remarkably elastic tissue, formed, apparently, of transverse little pillars, becoming fibrous on the outside, and with their inner ends appearing like hyaline points. The mouth of the acoustic sack (removed in the drawing) is closed by a tender diaphragm, through which I saw what I believe was a moderately-sized nerve enter; I have not yet succeeded in tracing this nerve. The first pair of cirri seem, to a certain extent, to serve as antennæ, and therefore the position of an acoustic organ at their bases, is analogous to what takes place in crustacea; but there are not here any otolites, or the siliceous particles and hairs, as described by Dr. Farre, in that class. Nevertheless, the sack is so highly elastic, and its suspension in a meatus freely open to the water, seems so well adapted for an acoustic organ, that I have provisionally thus called it. In the larva, as I have shown, a pouch, certainly serving for some sense, I believe for hearing, is seated in quite a different position at the anterior end of the carapace. I may mention that I found sessile Cirripedes very sensitive of vibrations in objects adjoining them, though not, apparently, of noises in the air or water. In a group of specimens, I could not touch one even most delicately with a needle, without all the adjoining ones instantly withdrawing their cirri; it made no difference if the one touched had its operculum already closed and motionless.

Reproductive System,—Male Organs.—All the Cirripedia which I have hitherto examined, with the exception of certain species of Ibla and Scalpellum, are hermaphrodite or bisexual.[17] I shall so fully describe the sexual relations of the several species of these two genera, under their respective headings, and at the end of the genus of Scalpellum, that I will not here give even an abstract of the grounds on which my firm belief is based, that the masculine power of certain hermaphrodite species of Ibla and Scalpellum, is rendered more efficient by certain parasitic males, which, from their not pairing, as in all hitherto known cases, with females, but with hermaphrodites, I have designated Complemental Males.

[17] I am compelled to differ greatly from the account given by Prof. Steenstrup of the reproductive system in the Cirripedia, in his 'Untersuchungen über das Vorkommen des Hermaphroditismus, ch. v, 1846;—a translation of which I have seen, owing to the great kindness of Mr. Busk. Mr. Goodsir has described ('Edin. New Phil. Journal,' July 1843,) what he considers the male of Balanus; but I have seen this same parasitic creature charged with ova, including larvæ! From the resemblance of the larvæ to the little crustacean described by Mr. Goodsir, in the same paper, as a distinct parasite, I believe the latter to be the male of his so-called male Balanus, and that all belong to the same species, allied to Bopyrus. This genus, as is well known, is parasitic on other crustacea; and it is a rather interesting fact thus to find, that this new parasite which is allied to Bopyrus, in structure, is likewise allied to it in habits, living attached to Cirripedia, a sub-class of the crustacea.

The male organs have been well described by M. Martin St. Ange, whose observations have since been confirmed by R. Wagner.[18] The testes are small, often leaden-coloured, either pear or finger-shaped, or branched like club-moss,—these several forms sometimes occurring in the same individual; they coat the stomach, enter the pedicels, and even the basal segments of the rami of the cirri, and in some genera occupy certain swellings on the thorax and prosoma, and in others the filamentary appendages: the testes seen in the apex in one of these appendages in Conchoderma, is represented in Pl. IX, fig. 5. The two vesiculæ seminales are very large; they lie along the abdominal surface of the thorax, and generally (but not in some species of Scalpellum) enter the prosoma, where their broad ends are often reflexed; here the branched vessels leading from the testes enter. The membrane of the vesiculæ seminales is formed of circular fibres; and is, I presume, contractile, for I have seen the spermatozoa expelled with force from the cut end of a living specimen. The two canals leading from the vesiculæ generally unite in a single duct at the base of the penis; but in Conchoderma aurita, half-way up it. The probosciformed penis, except in certain species of Scalpellum, is very long; it is capable of the most varied movements; it is generally hairy, especially at the end; it is supported on a straight unarticulated basis, which in Ibla quadrivalvis alone (Pl. IV, fig. 9 a), is of considerable length; in this species, the upper part is seen to be as plainly articulated as one of the cirri; in Alepas, the articulations are somewhat less plain, and in the other genera, the organ can be said only to be finely ringed, but these rings no doubt are in fact obscure articulations. In the females of Ibla Cumingii and Scalpellum ornatum, there is, of course, no penis.

[18] In 'Müller's Archiv,' 1834, p. 467. I have already several times referred to M. Martin St. Ange's excellent Memoir, read before the Academy of Sciences, and subsequently, in 1835, published separately.

Female Organs.—M. Martin St. Ange has described how the peduncle[19] is gorged with an inextricable mass of branching ovarian tubes, filled with granular matter and immature ova. In Conchoderma and Alepas, the ovarian tubes run up in a single plane (Pl. IX, fig. 3,) between the two folds of corium round the sack. Here the development of the ova can be well followed: a minute point first branches out from one of the tubes; its head then enlarges, like the bud of a tulip on a footstalk; becomes globular; shows traces of dividing, and at last splits into three, four, or five egg-shaped balls, which finally separate as perfect ova. Within the peduncle, the ovarian tubes branch out in all directions, and within the footstalks of the branches (differently from what takes place round the sack), ova are developed, as well as at their ends. Close together, along the rostral (i. e., ventral) edge of the peduncle, two nearly straight, main ovarian tubes or ducts may be detected, which do not give out any branches till about half way down the peduncle, where they subdivide into branches, which inosculate together, and give rise to the mass filling the peduncle, and sometimes, as we have just seen, sending up branches round the sack. These two main unbranched ovarian ducts, followed up the peduncle, are seen to enter the body of the Cirripede (close along side the great double peduncular nerves), and then separating, they sweep in a large curve along each flank of the prosoma, under the superficial muscles, towards the bases of the first pair of cirri; and then rising up, they run into two glandular masses. These latter rest on the upper edge of the stomach, and touch the cæca

where

such exist; they were thought by Cuvier to be salivary glands. They are of an orange colour, and form two, parallel, gut-formed masses, having, in Conchoderma, a great flexure, and generally dividing at the end near the mouth into a few blunt branches. I was not able to ascertain whether the two main ducts, coming from the peduncle, expanded to envelope them, or what the precise connection was. The state of these two masses varied much; sometimes they were hollow, with only their walls spotted with a few cellular little masses; at other times they contained or rather were formed of, more or less globular or finger-shaped aggregations of pulpy matter; and lastly, the whole consisted of separate pointed little balls, each with a large inner cell, and this again with two or three included granules. These so closely resembled, in general appearance and size, the ovigerms with their germinal vesicles and spots, which I have often seen at the first commencement of the formation of the ova in the ovarian tubes in the peduncle, that I cannot doubt that such is their nature. Hence I conclude, that these two gut-formed masses are the true ovaria. I may add, that several times I have seen in the two long, unbranched ducts, connecting the true ovaria and the ovarian tubes in the peduncle, pellets of orange-coloured cellular matter (i. e., ovigerms) forming at short intervals little enlargements in the ducts, and apparently travelling into the peduncle.

[19] I may here mention, that in all sessile Cirripedes, the ovarian branching tubes lie between the calcareous or membranous basis and the inner basal lining of the sack, and to a certain height upwards round the sack: the true ovaria and the two ducts occupy the same position as in the Lepadidæ.

The structure here described is quite conformable with that which we have seen in the larva; in the latter, two gut-formed masses of equal thickness extended from the cæca of the stomach to within the future peduncle, where the cement-ducts entered them, and where, after a short period, they were seen to expand into a mass of ovarian tubes. In the mature Cirripede, the cement-ducts can still be found united to the ovarian tubes in the middle of peduncle; and the cause of the wide separation of the true ovaria and ovarian tubes, can be simply accounted for by the internal, almost complete intersection of the animal, which takes place during the last metamorphosis.

The ova, when excluded, remain in the sack of the animal until the larvæ are hatched; they are very numerous, and generally form two concave, nearly circular, leaves, which I have called after Steenstrup and other authors, the ovigerous lamellæ (Pl. IV, fig. 2 b). These lamellæ lie low down on each side of the sack: in Conchoderma virgata, however, there is often only a single lamella, forming a deeply concave cup: in C. aurita there are generally on each side four lamellæ, one under the other. The ova lie in a layer from two to four deep; and all are held together by a most delicate transparent membrane, which separately enfolds each ovum: this membrane is often thicker and stronger round the margins of the lamellæ, where they are united, in a peculiar manner, presently to be described, to a fold of skin, on each side of the sack: these two folds, I have called the ovigerous fræna (Pl. IV, fig. 2 f).

M. Martin St. Ange, describes an orifice under the carina, by which he supposes the ova to enter the sack; this, after repeated and most careful examinations, I venture to affirm does not exist; on the contrary, I have every reason to believe that the ova enter the sack in the following curious manner. Immediately before one of the periods of exuviation, the ova burst forth from the the ovarian tubes in the peduncle and round the sack, and, carried along the open circulatory channels, are collected (by means unknown to me) beneath the chitine-tunic of the sack, in the corium, which is at this period remarkably spongy and full of cavities. The corium then forms or rather (as I believe) resolves itself into the very delicate membrane separately enveloping each ovum, and uniting them together into two lamellæ; the corium having thus far retreated, then forms under the lamellæ the chitine-tunic of the sack, which will of course be of larger size than the last-formed one, now immediately to be moulted with the other integuments of the body. As soon as this exuviation is effected, the tender ova, united into two lamellæ, and adhering, as yet, to the bottom of the sack, are exposed: as the membranes harden, the lamellæ become detached from the bottom of the sack, and are attached to the ovigerous fræna. To demonstrate this view, an individual should have been found, with both the old and new chitine tunic of the sack, and with the lamellæ lying between them; this, I believe, I have seen, but it was before I understood the full importance of the fact: a great number of specimens would have to be examined in order to succeed again, for the changes connected with exuviation supervene very quickly. I have, however, several times found the ova so loose under the sack, as to be detached with a touch from the ovarian tubes; and I have twice carefully examined specimens, which had just moulted, as shown by even the mandibles being flexible, in which the lamellæ had not become united to the fræna, but still adhered to the newly-formed chitine tunic of the sack; in these, the ova were so tender, that they broke into pieces rather than be separated from the membrane of the lamella, itself hardly perfectly developed, for pulpy cellular matter adhered outside some of the ova. These and other facts are quite inexplicable on any other view than that advanced.

As the lamellæ are formed without organic union with the parent, they would be liable to be washed out of the widely open sack of the Lepadidæ, if they had not been specially attached to the fræna. These fræna consist of a pair of more or less semicircular folds of skin, depending inside the sack, on each side of the point of attachment of the body. The fræna are often of considerable size, but in Ibla, they are very minute; they are formed of chitine tunic with underlying corium, like the rest of the sack; on their crests, there is a row, or a set of circular groups, or a broad surface, covered, either with minute, pointed, bead-like bodies mounted on long hair-like footstalks, or with staff-formed bodies on very short footstalks. I measured some of the bead-like bodies, in Lepas anserifera, and they were 1/2000th of an inch in diameter, and the footstalks three or four times as long as the elongated heads. These heads, of whatever shape they may be, have an opaque, and, I believe, glandular centre; I could not make out with certainty an aperture at their ends, but, I believe, such exists, and they seem to secrete a substance, which hardens into a strong membrane, serving to unite the crest of the frænum to the edges of the lamellæ. In one case, this bit of membrane seemed formed of a woven mass of threads. These little glandular bodies, with the membrane formed by them, are cast off at each exuviation, and new glands formed on the crest of the frænum underneath. In some species of Pollicipes, (viz., P. cornucopia and elegans,) the fræna, though present and large, are functionless and destitute of the glands: I believe, they exist in this same functionless condition, and in rather a different position in the sessile Cirripedes, and that in this family they serve as Branchiæ.

The above-described method by which Cirripedia lay their eggs, namely, united together in a common membrane, placed between their old outer and new inner integuments, and the manner in which the lamellæ, when thus formed, are retained for a time fastened to the fræna, and are then cast off, appears to me very curious. In some of the lower Crustacea, it is known, that the ova escape by rupturing the ovisacs formed by the protruded ovarian tubes, and this is the nearest analogy with which I am acquainted. The ova are impregnated (as I infer from the state of the vesiculæ seminales), when first brought into the sack, and whilst the membrane of the lamellæ is very tender: the long probosciformed penis seems well adapted for this end. In the male of Ibla Cumingii, which has not a probosciformed penis, the whole flexible body, probably, performs the function of the penis: in Scalpellum ornatum, however, the spermatozoa must be brought in by the action of the cirri, or of the currents produced by them. That cross impregnation may and sometimes does take place, I infer from the singular case of an individual, in a group of Balani, in which the penis had been cut off, and had healed without any perforation; notwithstanding which fact, larvæ were included in the ova.

Exuviation; Rate of Growth; Size.—I have had occasion repeatedly to allude to the exuviation of the Lepadidæ: with the exception of the genus Lithotrya,[20] in which the calcareous scales on the peduncle, together with the membrane connecting them, is cast off, neither the valves nor the membrane uniting them, nor that forming the peduncle with its scales and styles, are moulted; but the surface gradually disintegrates and is removed, perhaps sometimes in flakes, whilst new and larger layers are formed beneath. In Scalpellum, I ascertained that the new membrane, connecting together the newly-formed calcified rims under the valves of the capitulum, was formed as a fold, with the articulated spines which it bears, all adpressed in certain definite directions. This fold of new membrane, when the old membrane splits and yields, of course expands, and thus the size of the capitulum is increased. In the peduncle, lines of splitting can seldom be perceived, except, indeed, in the sub-globular, embedded, downward-growing peduncle of Anelasma, as described under that genus. I do not understand what determines the complicated lines of splitting of the old membrane between the several valves of the capitulum,—without it be simply, that along these lines alone, the old membrane is not strengthened by the new membrane being closely applied under it, the new being formed, as we have just said, in a fold, in order to allow of increase in size. Although, as I believe, there is strictly no exuviation in the outer membranes of mature Lepadidæ, it seems that narrow strips of membrane are cast off from between the valves, for the few first moults, after the final metamorphosis of the larva. I may here remark that, in most sessile Cirripedes, the outside membrane connecting the operculum and shell, is regularly moulted.

[20] The external integuments being moulted in Crustacea, but not in the Cirripedia, may appear, at first, an important difference: but we here see that non-exuviation is not universal amongst the Lepadidæ, and, on the other hand, according to M. Joly, ('Annales des Sciences Naturelles,' 2d series, Zoolog.), there is one true crustacean, the Isaura cycladoides, which has a persistent bivalve shell.

The delicate tunic lining the sack, (a mere duplicature of that thick one, forming the outside of the capitulum, and generally transformed into valves,) and the integuments of the whole body, are regularly moulted. With these integuments, the membrane lining the œsophagus, the rectum, and the deep olfactory pouches, and the horny apodemes of the maxillæ, are all cast together. I have seen a specimen of Lepas, in which, from some morbid adhesion, the old membrane lining one of the olfactory pouches had not been moulted, but remained projecting from the orifice as a brown shrivelled scroll. The new spines on the cirri (and on the maxillæ) are formed within the old ones; but as they have to be a little longer than the latter, and as they cannot enter these up to their very points, their basal portions are not thus included, but are formed, running obliquely across the segments of the cirri; and what is curious, these same basal portions are turned inside out, like the fingers of a glove when hastily drawn off. After the exuviation of the old spines, the new spines have their inverted basal portions drawn out from within the segments, and turned outside in, so as to assume their proper positions.

All Cirripedia grow rapidly: the yawl of H. M. S. Beagle was lowered into the water, at the Galapagos Archipelago, on the 15th of September, and, after an interval of exactly thirty-three days, was hauled in: I found on her bottom, a specimen of Conchoderma virgata with the capitulum and peduncle, each half an inch in length, and the former 7/20ths in width: this is half the size of the largest specimen I have seen of this species: several other individuals, not half the size of the above, contained numerous ova in their lamellæ, ready to burst forth. Supposing the larva of the largest specimen became attached the first day the boat was put into the water, we have the metamorphosis, an increase of length from about .05, the size of the larva, to an whole inch, and the laying of probably several sets of eggs, all effected in thirty-three days. From this rapid growth, repeated exuviations must be requisite. Mr. W. Thompson, of Belfast, kept twenty specimens of Balanus balanoides, a form of much slower growth, alive, and on the twelfth day he found the twenty-first integument, showing that all had moulted once, and one individual twice within this period. I may here add, that the pedunculated Cirripedes never attain so large a bulk as the sessile; Lepas anatifera is sometimes sixteen inches in length, but of this, the far greater portion consists of the peduncle. Pollicipes mitella is the most massive kind; I have seen a specimen with a capitulum 2.3 of an inch in width.

Affinities.—Considering the close affinity between the several genera, there are, I conceive, no grounds for dividing the Lepadidæ into sub-families, as has been proposed by some authors, who have trusted exclusively to external characters. In establishing the eleven genera in the Lepadidæ, no one part or set of organs affords sufficient diagnostic characters: the number of the valves is the most obvious, and one of the most useful characters, but it fails when the valves are nearly rudimentary, and when they are numerous: the direction of their lines of growth is more important, and fails to be characteristic only in Scalpellum: with the same exception, the presence or abscence of calcified or horny scales on the peduncle is a good generic character. For this same end, the shape of the scuta and carina, but not of the other valves, comes into play. In three genera, the presence of filamentary appendages on the animal's body is generic; in Pollicipes, however, they are found only on three out of the six species. The number of teeth in the mandibles, and the shape of the maxillæ, often prove serviceable for this end; as does more generally the presence of caudal appendages, and whether they be naked or spinose, uniarticulate or multiarticulate; in Pollicipes alone this part is variable, being uni-and multi-articulate; and in one species of Scalpellum they are absent, though present in all the others. The shape of the body, the absence or presence of teeth on the labrum, the inner edge of the outer maxillæ being notched or straight, the prominence of the olfactory orifices, the arrangement of the spines on the cirri, and the number and form of their segments, are only of specific value.

Comparing the pedunculated and sessile Cirripedes, it is, I think, impossible to assign them a higher rank than that of Families. The chief difference between them consists, in the Lepadidæ, in the presence of three layers of striæ-less muscles, longitudinal, transverse and oblique, continuously surrounding the peduncle, but not specially attached to the scuta and terga; and on the other hand, in the Balanidæ, of five longitudinal bundles of voluntary muscles, with transverse striæ, fixed to the scuta and terga, and giving them powers of independent movement. In the Lepadidæ, the lower valves, or when such are absent, the membranous walls of the capitulum, move with the scuta and terga when opened or shut; and the lower part of the capitulum is separated by a moveable peduncle from the surface of attachment; in the sessile Cirripedes, the lower valves are firmly united together into an immovable ring, fixed immovably on the surface of attachment. I will not compare the softer parts, such as the cirri and trophi, of the Lepadidæ with those of the Balanidæ, as my examination of this latter family is not fully completed: I will only remark, that there is a very close general resemblance, more especially with the sub-family Chthamalinæ.

Geographical Range; Habitats.—The Pedunculated Cirripedes extend over the whole world; and most of the individual species have large ranges, more especially, as might have been expected, those attached to floating objects; excepting these latter, the greater number inhabit the warmer temperate, and tropical seas. Of those attached to fixed objects, or to littoral animals, it is rare to find more than three or four species in the same locality. On the shores of Europe I know of only three, viz., a Scalpellum, Pollicipes, and Alepas. At Madeira (owing to the admirable researches of the Rev. R. T. Lowe), two Pæcilasmas, a Dichelaspis, and an Oxynaspis are known. In New Zealand, there are two Pollicipes and an Alepas, and, perhaps, a fourth form. From the Philippine Archipelago, in the great collection made by Mr. Cuming, there are a Pæcilasma, an Ibla, a Scalpellum, Pollicipes, and Lithotrya. Of all the Lepadidæ, nearly half are attached to floating objects, or to animals which are able to change their positions; the other half are generally attached to fixed organic or inorganic bodies, and more frequently to the former than to the latter. Most of the species of Scalpellum are inhabitants of deep water; on the other hand, most of Pollicipes,[21] of Ibla, and Lithotrya are littoral forms. The species of Lithotrya have the power of excavating burrows in calcareous rocks, shells, and corals; and the singular manner in which this is effected, is described under that genus. Anelasma has its sub-globular peduncle deeply embedded in the flesh of Northern Sharks; and I have seen instances of the basal end of the peduncle of Conchoderma aurita, being sunk into the skin of Cetacea; in the same way the point of the peduncle in the male of Ibla, is generally deeply embedded in the sack of the female. I believe in all these cases, the cementing substance affects and injures the corium or true skin of the animal on which the creature is parasitic, whilst the surrounding parts, being not injured, continue to grow upwards, thus causing the partial embedment of the Cirripede. In the case of Anelasma, we have growth at the end of the peduncle, and consequently downward pressure, and this may possibly cause absorption to take place in the skin of the shark at the spot pressed on.

[21] I am informed by Mr. L. Reeve that Pollicipes mitella is eaten on the coast of China; and Ellis states ('Phil. Trans.,' 1758) that this is the case with P. cornucopia on the shores of Brittany. It is well known that the gigantic Balanus psittacus on the Chilian coast, is sought after as a delicacy; and I am assured, by Mr. Cuming, that it deserves its reputation.

Geological History.—Having treated this subject at length, in the volume of the Palæontographical Society for 1851, I will not here enter on it: I will only remark, that the Lepadidæ or Pedunculated Cirripedes are much more ancient, according to our present state of knowledge, than the Balanidæ. The former seem to have been at their culminant point during the Cretaceous Period, when many species of Scalpellum and Pollicipes, and a singular new genus, Loricula, existed; Pollicipes is the oldest genus, having been found in the Lower Oolite, and, perhaps, even in the Lias. The fossil species do not appear to have differed widely from existing forms.

Genus—Lepas. Plate I.

Lepas. Linnæus.[22] Systema Naturæ, 1767.

Anatifa. Brugière.[23] Encyclop. Method. (des Vers), 1789.

Anatifera. (Lister) et plerumque Auctorum Anglicorum.

Pentalasmis. (Hill.) Leach. Journal de Physique, July, 1817.

Pentalepas. De Blainville. Dict. des Sci. Nat., 1824.

Dosima. J. E. Gray. Annals of Philosophy, vol. x, 1825.

[22] Linnæus, as is well known, included under this genus both the pedunculated and sessile Cirripedes. According to the rules of the British Association, the name Lepas must be retained for part of the genus; and as the sessile division was named Balanus, by Lister and Hill, even before the invention of the binomial system, and subsequently, in 1778, by Da Costa, and again, in 1789, by Brugière, there can be no question that Lepas must be applied to the pedunculated section of the genus. In this instance it is particularly desirable to recur to the Linnean name, as no other name has been generally adopted. Had not Lister and Sir J. Hill published before the binomial system, their names of Anatifera and Pentalasmis would have had prior claims to Lepas.

[23] The date of this publication is almost universally given as 1792, apparently caused by an error in the title-page of the First Part, which has consequently been cancelled. The First Part contains Anatifa and Balanus, and was published in 1789. The Second Part was published in 1792, and has a corrected title-page for the whole volume.

Valvæ 5, approximatæ: carina sursùm inter terga extensa, deorsùm aut furcâ infossâ aut disco externo terminata: scuta subtriangula, umbonibus ad angulum rostralem positis.

Valves 5, approximate: carina extending up between the terga, terminating downwards in an embedded fork, or in an external disc: scuta sub-triangular, with their umbones at the rostral angle.

Filaments seated beneath the basal articulation of the first cirri; mandibles with five teeth; maxillæ step-formed; caudal appendages uniarticulate, smooth.

Distribution.—Mundane; attached to floating objects.

Description.—Capitulum flattened, sub-triangular, composed of five approximate valves. The valves are either moderately thick and translucent, or very thin and transparent; and hence, though themselves colourless, they are often coloured by the underlying corium. Their surfaces are either smooth and polished, or striated, or furrowed, and sometimes pectinated. They are not subject to disintegration; they are generally naked, except on the borders, where they are coated, and held together by membrane; in L. fascicularis, however, the valves are covered with thin membrane, bearing very minute spines. The manner of growth of the valves will be best described under each. All the valves, even in the same species, are subject to considerable variation in shape, more especially the terga.

Scuta.—These valves are sub-triangular in outline, with the basal margin straight and rather short; and with occludent and tergo-carinal margins more or less protuberant; in L. fascicularis, however, the basal (Pl. I, fig. 6), and occludent margins are slightly reflexed and prominent. A ridge, generally runs from the umbo to the upper point. Internally, there is no conspicuous pit for the adductor muscle; under the umbones, there is generally either on both valves, or only on the right-hand side (Pl. I, fig. 1 c), a small calcareous projection or tooth, of variable size and shape, even in the same species; it is generally largest on the right-hand valve; these teeth at first sight appear to form a hinge, uniting the opposite scuta at their umbones, but this is not really the case, and their use appears to be only to give attachment to the membrane uniting the valves together, and to the peduncle. The basal margin is internally strengthened by a calcified rim, more or less developed. The umbones (and primordial valves when distinguishable,) are seated at the rostral angles; during growth the basal margin is not added to, and the occludent margin only to small extent; hence the main growth of the valve is at the upper end, and along the carina-tergal margin. In L. fascicularis, however, the basal reflexed margin is slightly added to beneath the umbo.

Terga,—flat, small compared with the scuta, usually of an irregular quadrilateral figure, with the two upper or occludent margins very short, in proportion to the two (carinal and scutal) lower margins; all the margins are nearly straight. The two occludent margins, generally meet each other at about right angles, forming a small triangular projection; in L. fascicularis, however, the occludent margin is formed by a single, slightly curved line. The umbones (and primordial valves when distinguishable) are not seated at the uppermost point, but at the angle where the carinal margin unites to the upper of the two occludent margins: during growth the terga are added to, both on the occludent and on the scutal margins, and slightly along the carinal margin; hence their growth is unequally quaqua-versal, except at one angle of the irregular quadrilateral figure.

Carina.—This is always very narrow and curved, concave within, often carinated and barbed exteriorly; it extends upwards between the terga for one half or two thirds of their length: at the lower extremity it ends (with the exception of L. fascicularis), in a small fork (Pl. I, fig. 1, a, b) rectangularly inflected and embedded in the membrane, beneath the basal margin of the scuta. From comparing this lower part of the carina in L. australis (fig. 5 a), with the same part in some of the species of the allied genus Pæcilasma, it would appear that the fork is formed by an oblong disc, more and more notched at the end, and with the rim between the two points more or less folded backwards: conformably with this view, in very young specimens of L. australis, instead of a large and sharp fork, there is a small disc. The only use of the fork appears to be to give firm attachment to the membrane uniting the valves and peduncle. In L. fascicularis, instead of a fork, there is a broad, oblong disc (figs. 6, 6 a), rectangularly inflected; it is much longer than the fork, in proportion to the upper part of the carina; the disc is not more deeply embedded than the upper part. The umbo (and primordial valve when distinguishable,) of the carina is seated just above the embedded fork (or disc in L. fascicularis), at the point where the inflection takes place; hence the main growth of the carina is upwards,—the fork, however, being of course, likewise added to at its point: in L. fascicularis, the growth is both upwards and downwards.

Peduncle and Attachment.—The peduncle is generally quite smooth: though with a high power its surface may be seen to be studded with minute beads, or larger discs, of yellowish and hard chitine; in the young of L. australis, and I suspect of some other species, it is covered with very minute spines. The peduncle in this genus attains its greatest development. The cement-tissue debouches, I believe, only through the functionless larval antennæ, except in one species, L. fascicularis, in which a ball of this substance is formed in a most peculiar manner round the peduncle (Pl. I, fig. 6), apparently for the purpose of serving as a float, as will be presently described.

Size and Colour.—The species of this genus are the largest of the Pedunculata, with the exception of some Pollicipes: even in the smallest species (L. pectinata), the capitulum sometimes attains a length of about half an inch. The peduncle varies much in length in the same species: in L. anatifera, it is occasionally above a foot long. The colours of L. anatifera, L. Hillii, and L. anserifera, are very bright and striking; the membrane bordering the valves and that round the top of peduncle in two of the species, is of the brightest scarlet-orange; the valves, owing to the underlying corium, are pale blueish-grey, and the interspaces between them dark leaden-purple. The cirri and trophi are generally dark purple or lead-colour.

Filamentary Appendages.—These are attached to beneath the basal articulation of first pair of cirri; they vary in the several species, from one to five or six on each side, the lowest being always the longest. Several of them are occupied by testes. In L. pectinata, generally, not even one is developed. They are subject to great variation in their proportional lengths, and in number, in the same species. These organs have generally been considered to serve as branchiæ; I see no reason to believe that they are more especially designed for this end, than is the general surface of the body.

Mouth.—The labrum is moderately bullate, the longitudinal diameter of this part equalling about one third, or half of that of the rest of the mouth. The palpi are moderately developed. The mandibles (Pl. X, fig. 5) have five teeth with the inferior point either broad, or very narrow and tooth-like. The maxillæ are step-formed (Pl. X, fig. 9); the first step is sometimes indistinct and curved; and in L. pectinata, all the steps vary much, and are more or less blended together. The outer maxillæ (like those at Pl. X, fig. 16), are internally clothed continuously with spines. The olfactory orifices are not at all prominent.

Cirri.—The first pair is placed near the second pair, and is of considerable length; the second has the anterior ramus thicker than the posterior ramus, and the segments brush-like; the segments (Pl. X, fig. 26) of the four posterior cirri bear from four to six pair of long spines, with a row of small intermediate spines: in the posterior cirri of L. australis the lateral rim spines are much developed; and in those of L. fascicularis, the usual pairs of large spines are lost in a broad triangular brush, formed by the increase of the lateral marginal, and intermediate spines.

Caudal Appendages (Pl. X, fig. 18 b), very small, either blunt or pointed, and quite destitute of spines.

The prosoma is well developed. The stomach is surrounded in the upper part by a circle of large branching cæca. The generative system is highly developed; the testes coating the whole of the stomach, entering the filamentary appendages and the pedicels of the cirri; the two ovigerous lamellæ contain a vast number of ova; they are united to rather large fræna, of which the sinuous margin supports either a continuous row or separate tufts of glands.

Distribution.—The species abound over the arctic, temperate and tropical parts of the Atlantic, Indian and Pacific Oceans, and are always, or nearly always, attached to floating objects, dead or alive. The same species have enormous ranges; in proof of which I may mention that of the six known species, five are found nearly all over the world, including the British coast; and the one not found on our shores, the L. australis, apparently inhabits the whole circumference of the southern ocean.

General Remarks and Affinities.—The first five species form a most natural genus; they are often sufficiently difficult to be distinguished, owing to their great variability. The sixth species (L. fascicularis) differs to a slight extent in many respects from the other species, and has considerable claims to be generically separated, as has been proposed by Mr. Gray, under the name of Dosima; but as it is identical in structure in all the more essential parts, I have not thought fit to separate it. As far as external characters go, some of the species of Pæcilasma have not stronger claims, than has L. fascicularis, to be generically separated; and I at first retained them altogether, but in drawing up this generic description, I found scarcely a single observation applicable to both halves of the genus; hence I was led to separate Lepas and Pæcilasma. If I had retained these two genera together, I should have had, also, to include the species of Dichelaspis and Oxynaspis; and even Scalpellum would have been separable only by the number of its valves; this would obviously have been highly inconvenient. Although some of the species of Pæcilasma so closely resemble externally the species of Lepas, yet if we consider their entire structure, we shall find that they are sufficiently distinct; as indirect evidence of this, I may remark that Conchoderma (as defined in this volume), includes two genera of most authors, and yet certainly comes, if judged by its whole organisation, nearer to Lepas than does Pæcilasma.

1. Lepas anatifera. Tab. I. fig. 1. (var.)

L. anatifera. Linnæus. Systema Naturæ, 1767.

Anatifa vel anatifera vel pentalasmis lævis[24], plerumque auctorum.

———— engonata (!).[25] Conrad. Journal Acad. Nat. Sc. Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 15.

———— dentata (var.) Brugière. Encyclop. Meth. (des Vers), 1789.

Pentalasmis dentatus (var.) Brown. Illust. Conch., Pl. lii, fig. 5.

Anatifa . . . . . . . . . . . . Martin St. Ange. Mem. sur l'organisation des Cirripedes, 1835.

[24] As this, though the commonest species, has never been defined, I give only a few synonyms and references, it being quite impossible to distinguish, in any published description, this species from A. Hillii of Leach; this latter species I recognise under this name only from having authentic specimens from the British Museum, as Leach overlooked every one of the real diagnostic characters.

[25] I have used, in conformity with botanists, the mark of interjection, to show that I have seen an authentic specimen.

L. valvis aut lævibus aut delicate striatis: è duobus scutis, dextro solùm dente interno umbonali instructo; pedunculi parte superiore fuscâ.

Valves smooth, or delicately striated. Right-hand scutum alone furnished with an internal umbonal tooth: uppermost part of peduncle dark-coloured.

Filaments, two on each side.

Var. (a). Fig. 1. Scuta and terga with one or more diagonal lines of dark greenish-brown, square, slightly depressed marks.

Var. (b). (Fig. 1 b.) Carina strongly barbed.

Extremely common; attached to floating timber, vessels, sea-weed, bottles, &c., and to each other, in the Atlantic Ocean, Mediterranean, West Indies, Indian Ocean, Philippine Archipelago, Sandwich Islands, Bass's Straits, Van Diemen's Land.

General Appearance.—Valves white, more or less translucent and thick, with a tinge of blueish-grey, from the underlying corium; sometimes brownish cream-coloured, rarely with a tint of purple. Surfaces smooth, with traces of very fine lines radiating from the umbones, sometimes rather plain on the basal part of the scuta. Length in proportion to the breadth of the capitulum variable, owing to the varying degree to which the scuta and terga have their apices produced. Scuta with the occludent margin either considerably curved or nearly straight. The internal tooth of the right-hand scutum, close to the umbo, varies in size and form, being either pointed, square, or obliquely truncated on either side, or it has a notch on the summit; internal basal rim of the scuta either plainly developed or nearly absent. In many specimens (Pl. I, fig. 1), on the scuta, or on the scuta and terga, (and sometimes more on one side of the individual than on the other,) a nearly straight line, running diagonally across the capitulum, of slight, quadrilateral depressions, of a dirty greenish colour, with the edges blending away, is either conspicuously developed, or can only just be discerned. These marks increase in size from the umbones to the margins of the valves. There are sometimes two or even three rows on the scuta. They are formed by the retention of a portion of the chitine membrane, which is cast off the rest of the surface; the margins of the valves are occasionally notched slightly on the line of marks; there is no difference along this line in the underlying corium. Specimens both with and without a barbed carina are thus characterised. Carina; the interspace between the carina and the scuta and terga is not wide. The carina exteriorly, is either convex and smooth, or furnished with knobs or with extremely sharp, long teeth (Pl. I, fig. 1 b); small specimens, with the capitulum under half an inch in length, are generally most strongly barbed.[26] Apex more or less acuminated; width and thickness variable; sides strongly furrowed. Fork (fig. 1 a) generally less wide than the widest upper part of the valve, with the two prongs diverging from each other at less than a right angle; their sharpness and precise form variable; rim between them reflexed (figs. 1 a and b), making a slight notch behind. Peduncle smooth, wrinkled, length in proportion to that of the capitulum varying, from barely equalling it, to six or seven times as long. I have noticed a specimen including mature ova, with a capitulum under half an inch long.

[26] Mr. W. Thompson found that 15 specimens, out of about 200, attached to a vessel which came from New Orleans into Belfast, had their carinas barbed.

Filamentary Appendages;—never more than two on each side, with sometimes only one developed; of variable length; one seated on the flank of the prosoma, under the first cirrus; the second close under the basal articulation of this cirrus, on the posterior face of a slight swelling: these appendages correspond with g and h in Fig. 4, Pl. IX.

Mouth.

—Mandibles (Pl. IX, fig. 5), with, as usual, five teeth, all pointing downwards. Maxillæ (Pl. IX, fig. 9), with the lower step of variable width compared to the two upper steps. Cirri; posterior cirri with segments (fig. 26) bearing six pair of spines; intermediate fine spines rather long; first cirrus, anterior ramus longer by only about two segments than the posterior ramus; second cirrus with anterior ramus, with very broad transverse rows of bristles; spine-bearing surfaces considerably protuberant; caudal prominences smooth, rounded.

Size.—The largest specimen which I have seen had a capitulum two inches in length; the longest, including the peduncle, was sixteen inches.

Colours.—Calcareous valves already described. Edges of the orifice bright scarlet orange; basal edges of the scuta, and sometimes of all the valves, with a torn border of orange membrane. Interspaces between the valves dull orange-brown. Peduncle darkish purplish-brown, with the lower part sometimes pale; chitine membrane itself tinted orange; in young specimens, peduncle pale, the colour first appearing in the uppermost part, close under the capitulum; this upper part is often darker than the other parts, and never orange-coloured, as in L. Hillii and L. anserifera. Sack internally dark purplish lead-colour, sometimes with a tinge of orange, darkest under the growing edges of the valves; body of animal pale purplish lead-colour. The four posterior cirri blackish purple; the second, and often the third cirrus, appear as if the colour had been laterally abraded off; these latter cirri have sometimes a tinge of orange. In very young specimens, the cirri are only barred with purple. The ova and the contents of the ovarian tubes are of a beautiful azure blue, becoming yellow in spirits.

In museums a vast amount of difference is seen in the colours of this species, caused by the method of preparation: if dried without having been in spirits, and subsequently kept dry, the orange tint round the orifice is preserved; if kept long in spirits, this is quite lost; but sometimes in specimens in spirits the colour of the membrane of peduncle is preserved and rendered pinker. The colours of the sack and animal are either quite discharged or rendered extremely dark. The valves themselves also often become more opaque. In some specimens well preserved in spirits, the sack and cirri were purplish-brown or lead-colour, tinted with dirty green, or orange, or bright yellow, or brick-red.

General Remarks.—From the foregoing description it will be seen how extremely variable almost every part of this species is. I find, in the British Museum, ten distinct specific names given by Dr. Leach to different varieties, or rather to different specimens, for some of them are undistinguishable. A specimen from the Sandwich Islands, sent by Mr. Conrad to Mr. Cuming, is marked A. engonata.

In looking over a large collection of specimens in a museum, the most distinctive characters appear at first to be the colours, the dentation or barbed condition of the carina, the row of square marks on the scuta and terga, and the more or less produced form of the whole capitulum: all these characters are absolutely worthless as distinctive characters, and blend into each other. In a fresh condition, the colours of this species, and of L. anserifera and L. Hillii are surprisingly alike, though in L. anatifera alone, the uppermost part of the peduncle is dark. As far as I have seen, the smoothness of the valves, together with the presence of a tooth beneath the umbo, on the right-hand scutum, and its entire absence on the left side, (in other species it is smaller on this, than on the right-hand side,) is an unfailing diagnostic mark. I believe this species is always attached to floating objects, though there are some very young specimens in the British Museum, collected by Sir G. Grey, adhering to sandstone, but this may have been buoyed up by some large sea-weed. Mr. Peach has given me the particulars of two instances, in which, after gales of wind, this species, of nearly full size, adhering to apparently freshly broken-off Laminariæ, has been cast upon the coast of England and Scotland.

2. Lepas Hillii. (Pl. I, fig. 2).

Anatifa vel pentalasmis lævis (!) plerumque auctorum.

Pentalasmis Hillii (!). Leach. Tuckey's Congo Expedit. p. 413, 1818.

—————— cheloniæ (!) Ib. Ib.

Anatifa tricolor (?). Quoy et Gaimard. Ann. des Sc. Nat., 1st series, tom. x, 1827, Pl. vii, fig. 7, et Voyage de l'Astrolabe, Pl. xciii, fig. 4.

———— substriata (!). Conrad. Journal Acad. Nat. Sc., Philadelphia, vol. vii, 1837, p. 262, Pl. xx, fig. 14.

L. valvis lævibus; scutorum dentibus internis umbonalibus nullis; carinâ à cæteris valvis, furcâ etiam a scutorum basali margine, paululum distante; pedunculi parte superiore aut pallidâ aut aurantiacâ.

Valves smooth; scuta destitute of internal umbonal teeth; carina standing a little separate from the other valves, with the fork not close to the basal margin of the scuta; uppermost part of peduncle either pale or orange-coloured.

Filaments three on each side.

Extremely common; attached to ships' bottoms, from all parts of the world; on floating timber; associated with L. anatifera and L. anserifera. Mediterranean. Attached to turtles, in the Atlantic, lat. 30° north. West Indies. Falkland Islands. "South Seas," collected by A. Menzies. Port Stephen, Australia.

General Appearance.—Capitulum laterally flat; length varies in proportion to the breadth; valves white, somewhat translucent, moderately thick, very smooth, but with faint traces of radiating lines; in some varieties, surface rather irregular along the zones of growth. Scuta without any internal teeth, and with scarcely any trace of the internal basal rim; upper angle little acuminated; the occludent margins of the two scuta stand rather separate from each other, showing a wide space of corium between them: these margins are arched and protuberant, but with the lower part a little hollowed out; basal margin a little curved. In one specimen alone, I saw a trace of a diagonal line of square coloured marks, like those common in L. anatifera. Terga rather broad, with the basal angle not much acuminated. The degree of prominence and outline of the double occludent margin varies very much. Carina, separated by a rather wide space from the scuta and terga; of very varying shape, the upper part not much acuminated, generally very flat, sometimes exteriorly marked by a central depressed line; never barbed; occasionally, (in a specimen from Australia,) middle part so wide as almost to become spoon-shaped; on the other hand occasionally of nearly the same width throughout; somewhat constricted above the fork. Fork deeply embedded as usual; situated, in fresh specimens, a little way beneath the basal margins of the scuta, instead of touching them, as in the other species; forks of varying width, not so abruptly inflected as in many species; sometimes much narrower than the upper widest part of the valve, sometimes nearly twice as wide; prongs of fork not very sharp, diverging at about a right angle, with the rim between them reflexed. The apex of the carina extends up between the terga for barely half their length, instead of up fully three fourths of their length, as in L. anatifera.

The chitine membrane at the base of the capitulum, especially at the anterior and posterior ends, is covered with beautiful, little, embedded, yellowish beads, about 3/2000th of an inch in diameter; above this, on each side of the carina, there is a space with similar but smaller little spheres, and still higher up still minuter ones; others occur on different parts of the capitulum; these spaces are seen to be distinctly separated from each other, and present a beautiful appearance under a high power.

Peduncle, as long as, or rather longer than, the capitulum: in one set of specimens, however, it was thrice or four times as long as the capitulum. The peduncle, in some specimens, was conspicuously covered with transverse plates of yellowish hard chitine.

Filamentary Appendages.—Three on each side; one on the flank of the prosoma, with a pair beneath the basal articulation of the first cirrus; relative lengths various, but the posterior filament of the pair under the cirrus, is the shortest. Mouth; palpi not much acuminated; maxillæ step-formed, but with the upper or first step in some specimens indistinct, or forming a curve. Cirri; the segments of the first cirrus and of the posterior arm of the second cirrus are highly protuberant, the protuberances sometimes equalling half the thickness of the segments themselves. Caudal appendages smooth, rounded.

Size.—The largest specimen which I have seen, in the collection of Mr. Cuming, had a capitulum 1-1/10th of an inch long, and 1-1/4 wide; therefore not quite equalling in size the largest specimens of L. anatifera.

Colours.—When fresh, valves blueish-grey from the underlying corium, edges of all the valves and round the orifice, and round the top of the peduncle, bright orange-yellow, passing into the finest scarlet, and varying slightly in tint in different specimens. Space between the carina and the other valves, and between the occludent margins of the scuta, rich purplish-brown; peduncle either pale or purplish-brown, or only clouded on the sides with the same. In young specimens, peduncle nearly colourless; and in those under a quarter of an inch long in the capitulum, the top of the peduncle has not acquired its orange tint. Sack pale, leaden-purple, body the same, but paler and more reddish; cirri (but only the tips of first pair) tinted with fine golden orange. Immature ova in peduncle beautiful blue. After being long kept in spirits, the colours are changed, weakened, or discharged, as in L. anatifera and L. anserifera, and the valves become opaque. In some long-kept specimens the corium everywhere had become pale brown; more usually it assumes a dirty purplish lead-colour.

Monstrous Variety.—Amongst a set of ordinary specimens from a ship from Genoa, sent me by Mr. Stutchbury, there were three, one full-grown and two very young, with the whole capitulum, (and likewise with the scuta and terga taken separately,) not above half the usual length in proportion to the breadth. Neither the colours nor animal in this variety presented any difference.

General Remarks.—This species is almost universally confounded with L. anatifera. Quoy and Gaimard, however, appear to have distinguished it, under the name of A. tricolor, from its colours. Leach named it accidentally, for he specifies not one distinctive character, and besides his two published names, he has appended two other names to specimens in the British Museum. A specimen, from the Sandwich Islands, sent by Mr. Conrad to Mr. Cuming, is marked A. substriata. In a dry state, from the shrinking of the membranes, and consequent approach of the carina to the other valves, and of the fork to the basal margin of the scuta, it is most difficult to distinguish this species, though so decidedly distinct, from L. anatifera; the absence, however, of a tooth on the under side of the right-hand scutum is at once characteristic. Even in specimens kept in spirits, in which there has been no shrinking, but in which the colours have changed, and taking into account the variation in the carina and upper part of the terga, this species is not always readily distinguished from L. anatifera, without opening the valves and looking for the right-hand tooth of the latter. In fresh specimens, the orange ring at the top of the peduncle, and the broad purplish interspace between the carina and other valves, are characteristic. In all states, the filamentary appendages offer a good character.

3. Lepas anserifera. Pl. I, fig. 4.

L. anserifera. Linnæus. Syst. Naturæ, 1767.

Anatifa striata. Brug. Encyclop. Meth. (des vers), Pl. clxvi, fig. 3.

Pentalasmis dilatata! (young). Leach. Tuckey's Congo Expedit., p. 413, 1818.

Anatifa sessilis (?). Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 11.

Lepas nauta.[27] Macgillivray. Edin. New Phil. Journ., vol. xxxviii, p. 300.

Pentalasmis anseriferus. Brown. Illust. Conch., 1844, Pl. li, fig. 1.

[27] Professor Macgillivray does not consider the species, which he has described under L. nauta, and which I cannot doubt is the same with the present species, as the L. anserifera of Linnæus; but I find it so named in all old collections, and it seems to agree very well with Linnæus's description. There has been much groundless confusion about this species; I have no hesitation in giving A. striata, of Brugière, as a synonym, though I have received from Paris the Lepas pectinata of this volume, named as the A. striata; and on the other hand, Poli has incorrectly called a common variety of L. pectinata by the name of L. anserifera.

L. valvis approximatis leviter sulcatis (tergis præcipuè); scuto dextro dente forti interno umbonali, lævo aut dente exiguo, aut merâ cristâ instructo; margine occludente arcuato, prominente: pedunculi parte superiore aurantiacâ.

Valves approximate, slightly furrowed, especially the terga; right-hand scutum with a strong internal umbonal tooth; left-hand with a small tooth, or mere ridge; occludent margin arched, protuberant: uppermost part of peduncle orange-coloured.

Filaments five or six on each side.

Var. (dilatata, young); valves rather thin, finely furrowed, often strongly pectinated; scuta broad, with the occludent margins much arched, making the space wide between this margin and the ridge connecting the umbo and the apex: carina often barbed.

Common on ships' bottoms from the Mediterranean, West Indies, South America, Mauritius, Coast of Africa and the East-Indian Archipelago. Central Pacific Ocean. China Sea. Chusan. Sydney. Attached to pumice, various species of fuci, Janthinæ, Spirulæ; often associated with L. anatifera and L. Hillii, and, in a young state, with L. fascicularis.

General Appearance.—Capitulum more or less elongated relatively to its breadth; in two specimens, with scuta of equal width, one was longer than the other by the whole of the occludent margin of the terga. Valves white, thick, (in young specimens sometimes diaphanous and thin,) closely approximate to each other; surfaces furrowed to a very variable amount. Terga generally more plainly furrowed than the scuta, of which the basal portion is generally less furrowed than the upper part; ridges, often rough, generally much narrower than the furrows: in half-grown specimens (var., dilatata of Leach,) the ridges are frequently denticulated, and there is even sometimes a row of bead-like teeth along the basal margins of the scuta. The ridges vary much, sometimes alternately wide and narrow; in two specimens of equal size, there were, in one, thirty-two ridges, and in the other only eighteen, on the scutum.

Scuta, with the occludent margin rounded and protuberant to a variable degree, but always leaving a rather wide space between the margin, and the ridge which runs from the umbo to the apex; apex pointed. Right-hand internal tooth considerably larger than that on the left, which is often reduced to a mere ridge; internal basal rim thick, sometimes furrowed along its upper edge, but of variable thickness, sometimes not extending as far as the baso-carinal angle. Terga, sometimes equalling, sometimes only two-thirds of, the length of the scuta; in young specimens, the two occludent margins form a right-angle with each other; in older specimens they form less than a right-angle, and hence the portion of valve thus bounded is unusually protuberant. Carina, within deeply concave; exterior sides finely furrowed longitudinally, generally denticulated; valve only slightly narrowed in above the fork, of which the prongs diverge at an angle of 90°, or rather more, and are wider than the widest upper part of the valve; rim between the prongs reflexed; the heel or external angle, just above the fork, sometimes considerably prominent. I have seen only a single large specimen with its carina barbed. In half-grown specimens, (var. dilatata, Leach,) the carina is often strongly barbed, with the upper point much acuminated, the fork about twice as wide as the widest upper part, and the prongs diverging at rather more than a right-angle. In some specimens, especially very young ones, there are at the base of the carina, above the fork, some strong, downward-pointed, inwardly-hooked, calcareous teeth; such occur also in some specimens along the basal margins of the scuta, two of these hooked teeth under the umbones of the scuta being larger than the rest: specimens conspicuously thus characterised came from the Navigator Islands; in these, I may add, the acutely triangular primordial valves were quite plain.

Peduncle, generally about as long as the capitulum; in young specimens generally short.

Filamentary Appendages, generally five, sometimes six, on each side; one is seated on the side of the prosoma, and the four others placed in pairs beneath the basal articulation of the first cirrus; the lowest posterior filament of the four generally is the largest. In young specimens, having a capitulum only half an inch long, the upper pair of the four often is not developed, or is represented by mere knobs. The mouth presents no distinctive characters. Cirri, with the longer ramus of the first pair almost equal to the shorter arms of the second pair; spine-bearing surfaces only slightly protuberant. Caudal appendages smooth, curved, pointed.

Size.—The largest specimen which I have seen, had a capitulum one inch and a half in length.

Colours.—The white valves are edged with bright orange membrane; and are so close to each other that no interspaces, coloured from the underlying corium, are left. Peduncle, dark orange-brown, with the uppermost part under the capitulum bright orange all round; the chitine membrane itself being thus coloured. Sack, internally, dark purplish lead-colour. Body and cirri, either nearly white or pale purplish-lead colour, with the arms of the second, third, and fourth cirri, and pedicels of the fifth and sixth, more or less tinted with orange. A specimen preserved during fourteen months in good spirits had only a tinge of orange left round the orifice and round the upper part of peduncle, and on the cirri. In some other specimens, badly preserved, the chitine membrane was quite colourless, and sack and cirri dirty lead-colour. Fresh ova, peach-blossom-red; immature ova, in ovarian tubes, pale pink.

Monstrous Variety.—In Mr. Stutchbury's collection, there was a specimen, with the scuta, broad, smooth, thin, and fragile, without any ridge running from the umbo to the apex, and with the occludent margin reflexed. This seemed caused by the shell having been attacked by some boring animal, and from having supported Balani. In the same specimen the first cirrus on one side was monstrously thick and curled; the second cirrus had its posterior ramus in a rudimentary condition. In Mr. Cuming's Collection, there are small specimens with the zones of growth overlapping each other, with thick irregular margins, and with the carina distorted.

This species has cost me much trouble: I have examined vast numbers of specimens, from a tenth to half an inch in length, attached to light floating objects, such as Janthinæ and Spirulæ from the tropical oceans, which all resembled each other, and slightly differed from the common appearance of L. anserifera: this variety is the Pentalasmis dilatata of Leach; and for a long time I considered it as a distinct species. It differs from L. anserifera, in the less thickness of the valves, in their being more finely and yet plainly furrowed; in the greater width of the scuta; and more especially, of that part of the valve lying between the occludent margin, and the ridge running from the umbo to the apex; in the less elongation of the area in the terga, bounded by the two occludent margins; and, lastly, in the less size of the whole individual. The trophi and cirri are absolutely identical. Lately, however, in carefully going over a great suite of specimens, all the above few distinctive characters broke down and insensibly graduated away; and I am convinced that this form is only a variety of L. anserifera; its different aspect being caused partly by youth, but chiefly, I suspect, from being attached to light objects floating close to the surface of the sea.

The Lepas anserifera can be distinguished by the slight furrows on its valves from all the other species, excepting L. pectinata: this latter species can be readily known, by the close proximity in the scuta of the occludent margin, and the ridge extending from the umbo to the apex; by its carina being very narrow above the fork; by the prongs of the fork diverging at an angle of from 135° to 180°; by the thinness of its valves; by the coarseness of the furrows on them; and lastly, by there being at most in L. pectinata only one filamentary appendage beneath the first cirrus.

4. Lepas pectinata. Pl. I, fig. 3.

Lepas pectinata. Spengler. Skrifter Naturhist. Selbskabet, 2, B. 2, H., 1793, Tab. X, fig. 2.

——— muricata (var.) Poli. Test. Utriusque Scicil., vol. i, Pl. vi, figs. 23, 29, 1795.

Lepas anserifera. Poli. Test. Utriusque Scicil., vol. i, Pl. vi, figs. 25-27.

——— sulcata. Montagu. Test. Brit., Pl. i, fig. 6, 1803.

Pentalasmis sulcata. Leach. Encyclop. Brit. Suppl., tom. iii, Pl. lvii, 1824.

——————— spirulæ (!) (var.) Leach. Tuckey's Congo Expedit. Appendix, 1818.

——————— radula (var.) et sulcatus. Brown. Illust. of Conchology, Pl. li, figs. 3-6, 1844.

——————— inversus. Chenu. Illust. Conchy., Pl. i, fig. 14.

Anatifa sulcata. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, figs. 18, 20.[28]

[28] I may add, that I have received many specimens incorrectly labelled A. striata, which is properly a synonym of L. anserifera.

L. valvis tenuibus, crassè sulcatis, sæpe pectinatis; scutorum cristâ prominente ab umbone ad apicem juxta marginem occludentem pertinente: furcæ carinalis cruribus inter angulos 135° et 180° divergentibus.

Valves thin, coarsely furrowed, often pectinated. Scuta with a prominent ridge extending, from the umbo to the apex, close to the occludent margin; fork of the carina with the prongs diverging at an angle of from 135° to 180°.

Filaments absent, or only one on each side.

Var. (Pl. I, fig. 3 a), upper part of the terga (bounded by the two occludent margins) produced and sharp; surface of all the valves often coarsely pectinated, and with the carina barbed.

Atlantic Ocean, from the North of Ireland to off Cape Horn; common, under the tropics; Mediterranean: attached to wood, cork, charcoal, sea-weed, a reed-like leaf, spirulæ, cuttle-fish bones, to a bottle together with L. anatifera; to a ship's bottom, Belfast, (W. Thompson.) Often associated with L. fascicularis. Montagu states ('Test. Brit.,' p. 18) that this species is sometimes attached to the fixed Gorgonia flabellum.

General Appearance.—The capitulum varies considerably in length compared to its breadth, caused chiefly by the greater or less production of the occludent portion of the terga; valves thin, brittle; the furrowed surface varies much in character, narrow and broad ridges often alternating; frequently each ridge (but more especially the ridge running from the umbo to the apex of each scutum, and sometimes that alone,) is covered with prominent, curled, flat, calcareous spines, giving the shell an appearance like that of many mollusca. Other specimens show no trace of these calcified projections. From the thinness of the valves and the depth of the furrows, the margins of the valves are sinuous. Scuta: the ridge running from the umbo to the apex is unusually prominent and curved; it runs very close to the occludent margin, so that, differently from in all the other species, only a very narrow space is left between this margin and the ridge. Internal teeth, under the umbones, either sharp and prominent, or mere knobs; sometimes that on the right side is much larger than that on the left; sometimes they are nearly equal; sometimes that on the left is scarcely distinguishable. Internal basal rim absent, or barely developed.

Terga: these valves have a conspicuous notch to receive the apex of the scuta; the two occludent margins either meet each other at a rectangle, or at a much smaller angle, causing the portion thus bounded to vary much in outline, area, and degree of prominence. This at first led me to think that the P. spirulæ of Leach, in which the point is very sharp and prominent, was a distinct species; but there are so many intermediate forms, that the idea must be given up. I may remark, that in all the species of Lepas, the upper part of the tergum seems particularly variable. The degree of acumination of the basal portion of the tergum also varies; the internal surface sometimes has small crests radiating from the umbo.

Carina, broad, within deeply concave; edges sinuous, externally sometimes strongly barbed; narrow above the fork, which latter is wider than the widest upper part of the valve; prongs sharp, thin, diverging at an angle of from 135° to 180°; the rim connecting the prongs not, or only slightly, reflexed.

Peduncle, narrow, shorter than the capitulum.

Filamentary Appendages, none, or only one, short, obtuse projection on each side, on the posterior face of the swelling under the first cirrus.

Mouth.—Mandibles, with the inferior point produced into a single pectinated tooth, rarely into two pectinated teeth; on one side of one specimen, there were only four instead of five teeth. Palpi very narrow. Maxillæ highly variable; they may be described as formed of five steps, of which the two lower ones are generally united into a single one, divided by a mere trace of a notch; or with the three lower steps blended into an irregular, projecting surface, and with even the fourth step indistinct. I have seen these two extreme forms on opposite sides of the mouth of the same individual,—on one side the maxillæ being regularly step-form, on the other the whole inferior part forming an almost straight edge, standing high up above the first notch or step which bears the two upper great spines.

Cirri.—First pair rather far removed from the second pair, with the longer ramus about three-fourths of the length of shorter ramus of second cirrus; spine-bearing surfaces, hardly at all protuberant; lateral marginal spines on the posterior cirri rather long; caudal appendages smooth, rounded, extremely minute: penis very spinose.

Size.—Capitulum in the largest specimen, six-tenths of an inch long; only a few arrive at this size.

Colours, after having been kept in spirits,—sack and cirri, especially first cirrus, clouded with pale purple; peduncle brownish; valves appear blueish in specimens not long preserved, but in specimens kept longer they become perfectly and delicately white.

General Remarks.—Under the head of L. anserifera, I have made some remarks on the diagnostic characters of this species. In the thinness of the valves,—form of the carina, with the rim connecting the prongs being not, or scarcely, reflexed,—and in the shortness and narrowness of the peduncle, there is some approach to L. australis, and thence to L. fascicularis. In the form of the maxillæ,—in one specimen having the mandible on one side bearing only four teeth,—and in the frequent absence of filamentary appendages, there is some approach to the genus Pæcilasma; but there is no such approach in the characters derived from the capitulum. We have seen that, as in so many other species of this genus, most of the parts are variable, and this is the case to a most unusual extent in the form of the maxillæ. Dr. Leach has attached eight specific names to the specimens preserved in the British Museum.

5. Lepas australis. Pl. I, fig. 5.

L. valvis glabris, tenuibus, fragilibus; scutorum dentibus umbonalibus utrinque internis; carinæ parte superiore latâ, planâ, suprâ furcam valdè constrictâ; furcæ cruribus latis, planis, tenuibus, acuminatis, intermedio margine non relexo.

Valves smooth, thin, brittle; scuta with internal umbonal teeth on both sides. Carina with the upper part broad, flat; much constricted above the fork, which has wide, flat, thin, pointed prongs, with the intermediate rim not reflexed.

Filaments, two on each side.

Common on Laminariæ in the whole Antarctic Ocean: Bass's Straits, Van Diemen's Land: Bay of Islands, New Zealand, lat. 35° S.: lat. 50° S., 172° W.: coast of Patagonia, lat. 45° S.: attached to bottom of H. M. S. Beagle, lat. 50° S., Patagonia: attached to a Nullipora, (I presume a drift piece,) British Museum.

General Appearance.—Capitulum rather obtuse and thick; valves thin, brittle, approximate, either white and transparent, or dirty-brown and opaque; or sometimes tinted internally with purple (perhaps the effects of being preserved in spirits); surface plainly marked by lines of growth, rarely marked with traces of lines radiating from the umbones. Scuta with teeth on both sides, nearly equal; internal basal rim rather wide, sometimes furrowed; basal margin considerably curved inwards. Terga rather wide; basal angle blunt; angle formed by the two occludent margins blunt and rounded. Carina (fig. 5 a) with the apex blunt, flat; the middle part generally very broad; much constricted above the fork, where it is internally deeply concave, and externally carinated; fork twice as broad as the broadest upper part of the valve; with the prongs flat, broad, thin, pointed, diverging at about an angle of 75°, with the intermediate rim not at all reflexed; the fork generally not deeply imbedded in the chitine membrane of the peduncle, so as to be quite easily visible externally; sometimes there is an internal, transverse, depressed line on the fork. In young specimens, with the capitulum about a quarter of an inch long, the fork of the carina is not developed, the lower slightly inflected portion consisting simply of an oval plate, twice as wide as the upper part. Until I had carefully examined a perfect series, showing the gradual changes in this part, I did not doubt that the young specimens formed a distinct species, and named it accordingly: the shortness of the penis first made me perceive that the specimens were immature. At this early age, I may add, the filamentary appendages were not developed. Peduncle either quite short, or as long as the capitulum, close under which it is considerably constricted all round.

Filamentary Appendages.—Two on each side; one long, tapering, placed on the prosoma (in one specimen represented by a mere knob), and the second shorter, situated on the posterior margin of the swelling beneath the first cirrus.

Mouth.—Maxillæ, with three large spines at the upper angle, and with the first step distinct, but narrow; mandibles with five teeth; in young specimens the inferior point ends in a single spine; sides of the supra-oral cavity very hairy; the membrane, forming the inner fold of the labrum, yellow and thickened in the form of a spoon.

Cirri.—In the posterior cirri there are, at the upper lateral edges of the segments on both sides, small spines; the segments in the first cirrus, and in the broad anterior ramus of the second cirrus, are hemispherically and considerably protuberant. Caudal appendages smooth.

Size.—The largest specimen had a capitulum one inch long.

The Colours (after having been long in spirit) of the valves have already been given; sack and peduncle dirty yellowish-brown, with the parts corresponding to the margins of the valves much darker brown, or almost black; segments of the cirri clouded with dark brown; body and pedicels of the cirri dirty yellowish. I have reason to believe that the colours are totally different in living specimens.

Monstrous Varieties.—Most of the specimens from lat. 50° S., on the coast of Patagonia, were more or less deformed, with the successive zones of growth overlapping each other, and forming coarse concentric ridges. The carina in several specimens was laterally distorted.

I have already remarked that this species has some affinity to L. pectinata; but it is much more closely related to L. fascicularis, the affinity being clearly shown by the thinness and translucency of the valves, their convexity, by the width and little acumination of the upper part of the carina, by the width of the fork, and by its not being deeply imbedded. In young specimens, moreover, before the fork is fully developed, there is a remarkable similarity between the two species, in the form of this lower part of the carina. Again, the narrowness and inflection of the peduncle under the capitulum in L. australis, and lastly, the lateral marginal spines on both sides of the segments of the posterior cirri, all clearly indicate this same affinity to L. fascicularis.

I believe this species is confined to the southern ocean; and perhaps there represents L. fascicularis of the northern and tropical seas. It must, judging from the number of specimens brought home by Captain Sir J. Ross, and from those previously in the British Museum, and from those collected by myself, be a very common species.

6. Lepas fascicularis. Pl. I, fig. 6.

Lepas fascicularis. Ellis and Solander. Zoophytes, 1786, Tab. xv, fig. 5.

——— ———— Montagu. Test. Brit. Suppl., 1808, pp. 5, 164.

——— cygnea. Spengler. Skrifter Naturhist. Selbskabet, Bd. i, 1790, Tab. vi, fig. 8.

——— dilata. Donovan. British Shells, 1804.

Pentalasmis fascicularis. Brown. Illust. Conch., 1844, Pl. li, fig. 2.

————— spirulicola (!) et Donovani (!) Leach. Tuckey's Congo Expedit., p. 413, 1818.

Anatifa vitrea. Lamarck. Animaux sans Vertebres.

Dosima fascicularis. (!) J. E. Gray. Annals of Philosophy, vol. x, 1825.

Pentalepas vitrea. Lesson. Voyage de la Coquille. Mollusca, Pl. xvi, fig. 7, 1830.

Anatifa oceanica (!) Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii.

L. valvis glabris, tenuibus, pellucidis; carinâ rectangulè flexâ, parte inferiore in discum planum oblongum expansâ.

Valves smooth, thin, transparent; carina rectangularly bent, with the lower part expanded into a flat oblong disc.

Filaments, five on each side; segments of the three posterior cirri with triangular brushes of spines.

Var. (Donovani, of Leach.) Carina with the upper part flat, spear-shaped, externally with a narrow central ridge.

Var. (Villosa. Pl. I, figs. 6 b, c.) Valves placed rather distant from each other; carina extremely narrow, with the upper part of nearly the same width throughout; terga with the lower part much acuminated; body of animal finely villose.

Coasts of Great Britain and France; Baltic Sea, according to Montagu Southern United States (from Agassiz); tropical Atlantic Ocean; East-Indian Archipelago, off Borneo and Celebes; Pacific Ocean, between the Sandwich and Mariana Archipelagos; New Zealand: attached to fuci, Spirulæ Janthinæ, Velellas, often to feathers and cork; often associated with the young of L. anserifera, (var. dilatata,) and L. pectinata.

General Appearance.—Capitulum highly variable in all its characters; thick and broad in proportion to its length, but the breadth is variable,—in some specimens, the capitulum being longer by one-fifth of its total length than broad; in others, one-fifth broader than long. Valves generally approximate; in some varieties, however, from the narrowness of the carina and terga, the valves stand far apart, there being an interval between the carina and scuta of nearly half the breadth of the latter. Valves excessively thin, brittle, transparent, colourless, smooth, but generally sinuous along the zones of growth, which are conspicuous: valves generally covered throughout by thin chitine membrane, which is thickly clothed, especially in the interspaces between the valves, with minute spines, barely visible to the naked eye. Scuta with the lower part of the tergo-carinal margin extremely protuberant; occludent margin, more or less, but slightly reflexed, with a depressed line running from the umbo to the apex; basal margin much reflexed, but to a variable extent and at a varying angle, even up to a right angle,—an external rim or collar being thus formed. There are no distinct internal teeth, but the basal margin under the umbones, is more or less distinctly produced into a rounded disc or projection, which is generally not so much outwardly reflexed as the rest of the basal margin: there is no distinct internal basal rim. The primordial valves are generally visible, but they do not lie, as in all other species, close to the basal margin, but a little above it,—the lower reflexed portion having been subsequently developed. Terga flat, with the occludent margin slightly arched, and not, as in the foregoing species, formed of two sides; apex bent towards the carina; width of the lower half highly variable, owing to the varying extent to which the scutal margin is hollowed out; in some specimens, the whole lower half beneath the apex of the scuta is of nearly the same width throughout; in other specimens this lower part is spear-shaped. The widest part of the tergum either equals in width, or is only two-thirds of the width of the widest part of the carina beneath its umbo. Carina (Pl. I, fig. 6 a) highly variable in shape, with the part above the umbo either spear-shaped and slightly concave within, or nearly flat and furnished with a central external ridge; or the upper part (fig. 6 c) is of equal and extreme narrowness throughout, and deeply concave within, appearing as if only the central ridge had been developed. The part below the umbo, (answering to the fork in the foregoing species,) is about one-third of the length of the whole valve, and generally twice as wide as the upper part, but in the variety with the upper part of the carina equally narrow throughout, the lower part is thrice as wide as the upper; the disc, or lower part, is generally slightly concave within, exteriorly either with or without a central ridge; basal margin rounded; lateral margin more or less curved, according to the form of the upper part. The disc is not more deeply imbedded in membrane than is the upper part of the valve. The heel or umbo is either angular and prominent, or rounded. In very young specimens the carina is simply bowed, instead of being rectangularly bent.

Peduncle,—short, narrow, being abruptly inflected all round under the basal edges of the capitulum; lower part of very variable shape, being often suddenly contracted into a mere thread (fig. 6 b), which sometimes widens again at the extreme end. The external membrane is very thin, and is penetrated by the usual fine tubuli leading to the corium; its surface is wrinkled and destitute of spines, or with extremely few. The peduncle is often completely surrounded by a yellowish ball, (of which I have seen specimens from the coast of England, and from off Borneo,) sometimes half as wide as the capitulum, composed of very tender, vesicular, structureless membrane, and of a pulpy substance: perhaps the yellow colour may be owing to long immersion in spirits. Some authors have supposed that the ball was the ovisac of the animal; and for the first few minutes, deceived by the numerous included spores of, as I believe, Bacillariæ, I thought that this was the case; others have supposed that it consisted of some encrusting algæ or other foreign organism; but it is, in reality, a most singular development of the cement-tissue, which ordinarily serves to attach Cirripedes by their bases to some extraneous object, but here surrounding that object and the peduncle, gives buoyancy, by its vesicular structure, to the whole. The membrane of the ball falls to pieces in caustic potash, differently from the chitine membrane of the enclosed peduncle, and this shows that there is some difference in composition from ordinary cement. The ball, when cut in two, exhibits an obscure concentric structure. The whole is excreted by the two cement-ducts, through two rows of orifices, one on each side of the surrounded portion of the peduncle; and I actually traced, in one case, the yellow pulpy substance coming out of the cement-ducts. The upper apertures are in gradation larger than those below them, and they stand a little further apart from each other; these are figured as seen from the outside, much magnified, at Pl. I, fig. 6 d. I did not succeed in finding the cement-glands, but I followed the ducts, of rather large size, running for a considerable distance as usual along and within the longitudinal muscles of the peduncle. Nearly opposite the uppermost aperture, on each side, the duct passes out through the corium, and becomes laterally attached to the outer membrane of the peduncle, at which point an aperture is formed (as in other cases, by some unknown process), thus giving exit to the contents of the duct. Beneath this upper aperture the duct runs down the peduncle, between the corium and the outer membrane, till it comes to the next aperture, to which it is also attached, and so on to all the lower ones; but I believe no cement tissue continues to pass out through these lower apertures. Beneath the lowest aperture the two ducts run into the two prehensile antennæ of the larva, which, as usual, terminate the peduncle. The antennæ are attached to some small foreign body in the centre of the vesicular ball, by the usual tough, light brown, transparent cement. The two upper apertures are nearly on a level with the outside surface of the ball; and it was evident that as the animal grows, new apertures are formed higher and higher up on the sides of the peduncle, and that out of these, fresh vesicular membrane proceeds, and grows over the old ball in a continuous layer. It appears that the growth of the vesicular ball is not regular,—that it is not always formed,—and that when formed the whole, or the lower part, sometimes disintegrates and is washed away. As that portion of the peduncle which is enclosed ceases to grow, and has its muscles absorbed, retaining only the underlying corium, whereas the upper unenclosed portion, and likewise, (as it appears) lower portions once enclosed but since denuded, continue to increase in diameter, the peduncle, when the vesicular ball is removed, often has the most irregular outline, contracting suddenly into a mere thread, and then occasionally expanding again at the basal point.

Frequently two or three specimens have their peduncles imbedded in one common ball, of which there is a fine specimen in the College of Surgeons (Pl. I, fig. 6), the ball being about one inch and a quarter in diameter, with a slice cut off. In this specimen, it is seen that the vesicular membrane proceeding from several individuals, unites to form one more or less symmetrical whole, and that the original common object of attachment is entirely hidden. Dr. Coates[29] gives a curious account of the infinite number of specimens, through which he sailed during several days, in the Southern Atlantic Ocean: the balls appeared like bird's eggs, and were mistaken for some fucus, which was supposed to have encrusted the scales of the Velellæ, to which the Cirripede had originally become attached. Several individuals had their peduncles imbedded in the same ball, "which floated like a cork on the water." As this species grows into an unusually bulky animal, we here see a beautiful and unique contrivance, in the cement forming a vesicular membranous mass, serving as a buoy to float the individuals, which, when young and light, were supported on the small objects to which they originally had been cemented in the usual manner.

[29] Journal of the Acad. Nat. Sc., Philadelphia, vol. vi, p. 138, 1829.

Filamentary Appendages.—Five on each side, of which four lie in pairs at the base of the first cirrus (of these, only three are sometimes developed), and one on the flank of the prosoma.

Mouth.—Palpi much acuminated. Mandibles with five teeth; the first not far remote from the second; inferior point rather broad and finely pectinated. Maxillæ with two large, unequal, upper spines, and four regular steps.

Cirri.—Posterior cirri, with the upper parts of the segments slightly protuberant; in young specimens, the spines can be seen to consist of five pairs, placed in two converging lines in the upper half of each segment, with numerous minute, latero-marginal, and intermediate little bristles: in large specimens, all these latter have so increased in number, that the normal five pair cannot be distinguished, and the front of each segment is covered by a triangular thick brush of bristles, all pointing in the same direction, thus giving a very unusual character to the posterior cirri: the dorsal tuft on each segment consists of six or seven large spines, with from one to three dozen fine ones. First cirrus and anterior ramus of second cirrus with broad brushes of bristles. The pedicels of all the cirri are thickly covered with bristles. Caudal appendages smooth, with rounded summits.

Penis very hairy: vesiculæ seminales purple, much convoluted, lying within the prosoma; testes dendritic, scarcely enlarged at their terminal points, purplish; ovigerous fræna large with sinuous margins, the glandular beads being arranged in groups.

Size.—The largest specimen (from the coast of Devonshire) had a capitulum 1.6 of an inch long, and 1.2 broad, and of unusual thickness.

Colours, after having been in spirits: front surfaces of the segments of the cirri and of the pedicels purple. In some specimens from off Borneo, parts of the sack and the interspaces between the two scuta, were of a fine purple. Montagu states, that the whole shell and body of animal, when fresh, are pale blue, with the cirri spotted with brown.

General Remarks.—The extreme variability of this species is remarkable. In the College of Surgeons, there is a group of specimens collected by Mr. Bennett, I believe, in the Atlantic, in which the extreme narrowness of the carina and of the terga (Pl. I, fig. 6, b, c) (with consequent wide spaces of membrane left between these valves), led me, at first, to entertain no doubt, that it was quite a distinct species, which was strengthened by finding that the whole surface of the cirri were villose, with very minute spines; hence I called this variety, villosa. On the closest examination, however, I could detect no other differences, and the narrowness of the carina and terga varied very considerably: moreover, in one of the specimens, which was about intermediate in the form of its valves between this variety and the common form, the surfaces of the cirri were not in the least degree villose. Again, in some other specimens, the terga were as narrow as in Mr. Bennett's, whilst the carina had its usual outline.

In a var. (called by Leach, P. Donovani,) from the Atlantic, under the Equator, the carina is remarkable from the extreme flatness of the upper part, and from the presence of an exterior, narrow, central ridge. In one specimen from Jersey, in the British Museum, the carina made an extremely near approach to this same form.

Affinities.—This species is certainly much the most distinct of any in the genus, and Mr. Gray has proposed to separate it under the name of Dosima; but considering the close similarity of the whole organisation of the internal parts, together with the transitional characters afforded by L. australis, I think the grounds for this separation are not quite sufficient. I have remarked, under L. australis, on the affinity between that and the present species. In the carina terminating in a disc (though here not imbedded), there is some slight affinity to Pæcilasma eburnea and crassa, and markedly so in the arrangement of the bristles on the posterior cirri. In the valves being covered with villose membrane, and to a certain extent in the form of the carina and of the occludent margin of the terga, and especially in the two rows of cement-orifices in the peduncle, there is some affinity to Scalpellum.

Pæcilasma. Nov. Genus.[30] Plate II.

Anatifa. J. E. Gray. Proc. Zoolog. Soc., 1848, p. 44.

Trilasmis. Hinds. Voyage of the Sulphur. Mollusca, 1844.

[30] [Greek: Pokilos], various, and [Greek: elasma], plate or valve. I have not been able to adopt Mr. Hinds' name for this genus, as it would be too glaringly incorrect to call a five-valved species, a Trilasmis.

Valvæ, 3, 5, aut 7, approximatæ: carina solùm ad basales apices tergorum extensa, termino basali aut truncato aut in discum profunde infossum producto: scuta pænè ovalia, umbonibus ad angulum rostralem positis.

Valves, 3, 5, or 7, approximate: carina extending only to the basal points of the terga; with its lower end either truncated or produced into a deeply imbedded disc. Scuta nearly oval, with their umbones at the rostral angle.

Mandibles with four teeth; maxillæ notched, with the lower part of edge prominent; anterior ramus of the second cirrus not thicker than the posterior ramus; caudal appendages uniarticulate, spinose.

Generally attached to Crustacea.

I have already given my reasons for instituting and separating this genus from Lepas; as far as the capitulum is concerned, the differences between these genera certainly appear trivial; they consist in the carina not extending up between the terga, and in the lower end being either truncated, or produced into an imbedded disc: the terga have a single occludent margin. The included animal's body differs in more important respects; for both mandibles and maxillæ are very distinct; the cirri of some of the species also differ; and the caudal appendages are here always spinose: there are no filamentary appendages: and lastly, the habits are different.

The genus may be divided into two sections, firstly, P. Kæmpferi and P. aurantia, which have their carinæ basally truncated, the basal angles of their terga cut off, and the anterior rami of their second cirri shorter than the posterior rami; and, secondly, P. crassa, P. fissa, and P. eburnea, which in these several respects are otherwise characterised. The P. eburnea, however, differs rather more from P. crassa and P. fissa, than these two do from each other; but certainly not enough to allow of the retention of Mr. Hinds' genus of Trilasmis. P. crassa, in an especial degree, connects together all the forms.

General Appearance.—Capitulum oval, more or less produced, flat or gibbous; formed of three, five, or seven approximate valves; the lesser number arising from the abortion of the terga, and the greater number from the scuta being divided into two segments. Valves moderately thick, either white or reddish, smooth or striated, and sometimes partly covered by membrane, bearing minute spines. Scuta oval, of varying proportions; the basal margin is generally narrow, and blends into the carina-tergal margin; the internal basal rim generally is well developed, sometimes with, and sometimes without internal teeth beneath the umbones. In P. eburnea, and sometimes in P. crassa, there is a line of apparent fissure, and in P. fissa of actual disseverment, running from the umbo to the apex of each scutum, nearly in the line in which a ridge extends in Lepas: the primordial valves of the scuta in these three species, are seated at the basal angles of the lateral and larger segments. The positions of the primordial valves, and the direction of growth in the calcified valves, are, in all the species, the same as in Lepas. In several of the species attached to Crustacea, the two scuta are unequally convex, which is caused, as was pointed out to me by Mr. Gray, by that valve which lies close and nearly parallel to the body of the crab, being least developed. The Terga are either quite absent, or rudimentary as in P. crassa, or pretty well developed as in the other species: the occludent margin is single, and not double as generally in Lepas; the basal angle is either pointed or truncated. The Carina varies considerably in shape, but never extends up between the terga, nor ends downwards in a fork; in the first two species it is truncated; in the others, it terminates in a deeply-imbedded oblong disc, which in P. eburnea seems almost entirely (but of course not quite) to separate the inside of the capitulum from the peduncle; a similar separation is effected in P. fissa, where the imbedded disc is small, by two large teeth on the internal basal rims of the two scuta. The carina is always narrow, and either solid internally or very slightly concave.

Peduncle, is very short and narrow; the membrane is generally ringed with thicker, yellower portions, and often bears very minute spines.

Size.—All the species are small, with a capitulum not exceeding half an inch in length.

Filamentary Appendages.—None.

Mouth.—Labrum generally considerably bullate in the upper part, with a row of teeth on the crest. The mandibles have four teeth, with the inferior point narrow and spine-like, or rudimentary and absent. The maxillæ have, under the two or three upper great spines, a deep notch itself bearing spines; beneath this, the lower part is straight and considerably prominent, Pl. X, fig. 15. Outer maxillæ are covered on their inner sides continuously with spines.

Cirri.—The first pair is sometimes seated very distant from the second. The arrangement of the spines on the posterior cirri varies, to an unusual degree within the limits of the same genus. We have either the ordinary structure of anterior pairs, with single fine intermediate spines (as in P. Kæmpferi and aurantia), or we have the pairs increased by one or two additional longitudinal lateral rows, as in P. eburnea; or we have the front spines forming a single transverse row, as in P. crassa and P. fissa, Pl. X, fig. 29, a. The segments in none of the species are protuberant; the anterior ramus of the second cirrus does not seem to be thicker than the posterior ramus, as is usually the case. The rami of the second, and of most of the other cirri, are unequal in length,—the anterior ramus, contrary to the ordinary rule, being longer in P. eburnea, P. fissa, and P. crassa, than the posterior ramus by several segments; I have hitherto observed this inequality only in the sessile genus Chthamalus.

The Caudal Appendages are small, uniarticulate, and always furnished with bristles.

Distribution.—Four out of the five species live attached to Crustacea in the European and Eastern warmer temperate and tropical oceans; the fifth species was found attached to the dead spines of an Echinus, off New Guinea. It is probable that several more species will be hereafter discovered.

1. Pæcilasma Kæmpferi. Pl. II, Fig. 1.

P. valvis 5; carinæ basi truncatâ et cristatâ: scutorum dentibus internis umbonalibus fortibus: tergorum acumine basali truncato, margini occludenti pæne parallelo.

Valves 5; carina with a truncated and crested base; scuta with strong internal umbonal teeth; terga with the basal point truncated, almost parallel to the occludent margin.

Maxillæ with short thick spines in the notch under the two upper great spines; caudal appendages with scattered bristles on their summits, and along their whole outer margins.

Japan; attached, in great numbers, to the upper and under sides of the Inachus Kæmpferi of De Haan, a slow-moving brachyourous crab, probably from deep water. British Museum.

General Appearance.—Capitulum rather compressed, narrow, and produced. Valves white, tinged with orange, smooth, moderately thin, occasionally with faint traces of striæ radiating from the umbones. Scuta, apex pointed, with a very slight ridge running to the umbo; basal margin equalling two thirds of the length of the terga, with an internal basal rim; on the under side of each valve, beneath the umbo, there is a strong tooth. Out of the numerous specimens, all excepting one had their scuta unequally convex, with their occludent margins unequally curved, that of the more convex valve at the umbo, curling beyond the medial line. The basal end of the carina is, likewise, slightly curved laterally, and always turns towards the more convex valve. This inequality, as Mr. Gray pointed out to me, depends on the position of the specimens; the flatter side lying close to the carapace of the crab. Terga, flat, oblong, nearly rectangular; occludent margin straight; basal angle, truncated, almost parallel to the occludent margin; in width, three or four times as wide as the carina. Carina, (fig. 1, a) short, narrow, slightly curved, upper part broadest, with the apex rounded, only just passing up between the basal broad ends of the terga; externally carinated, internally very slightly concave; basal end abruptly truncated, crested, not deeply imbedded in the membrane of the peduncle.

Peduncle, barely as long as the capitulum, apparently (for specimens dry and much shrunk) narrow, surrounded by rings or folds of thicker yellowish membrane, of which the upper ones retain moderately long spines; low down these rings become confluent; whole surface finely dotted, dots largest on the rings.

Mouth.—Labrum highly bullate in the upper part, with a row of teeth on the crest; mandibles with four teeth, the fourth close to the inferior apex, which is very little developed, sometimes making the fourth tooth appear simply bifid. Maxillæ with two large spines on the upper angle, beneath which there is a large depression, bearing one rather long and thick, and four short and thick, spines; inferior upraised part with a double row of longer and thinner spines.

Cirri.—Posterior cirri with segments bearing five pairs of spines, of which the lowest pair is very minute; intermediate spines minute; spines of the dorsal tuft thin, of nearly equal size; segments not at all protuberant, elongated. First cirrus, standing far separated from the second (as in Scalpellum), with its nearly equal rami rather above half as long as those of the second cirrus. Second cirrus with anterior ramus not thicker, and scarcely more thickly clothed with spines, than the posterior ramus, but shorter than it by three or four segments; the spines not forming a very thick brush on the anterior ramus. Both rami of third cirrus with a longitudinal row of minute spines, parallel to the main pairs. Between the bases of the pedicels of the first pair of cirri, there are two closely approximate, conical flattened protuberances, like the single one to be described in Ibla.

Caudal Appendages, about one third of the length of the pedicel of the sixth cirrus, with some moderately long and strong spines at the end, and down the whole outer sides.

Ova, much pointed. Penis, hairy.

Size.—Capitulum in largest specimens half an inch long.

2. Pæcilasma aurantia. Pl. II, Fig. 2.

P. valvis 5; carinæ basi truncatâ: scutis ovatis, margine basali perbrevi, dentibus parvis, internis, umbonalibus instructo: tergorum acumine basali perobliquè truncato.

Valves 5; carina with a truncated base; scuta oval, with the basal margin very short, furnished with small internal umbonal teeth; terga, with the basal point very obliquely truncated.

Maxillæ with fine spines in the notch under the three great upper spines; caudal appendages with scattered bristles on their summits, and along only the upper part of their outer margins.

Madeira; found by the Rev. R. T. Lowe, attached to the rare Homola Cuvierii, probably a deep-water crab. British Museum.

General Appearance.—This species so closely resembles P. Kæmpferi, that it is superfluous to describe it in detail; and I will indicate only the points of difference. When the valves have been well preserved, they are of fine pale orange colour, and hence the name above given, which was proposed by the Rev. R. T. Lowe.

Scuta, with the internal umbonal teeth small; basal internal marginal rim very prominent, furrowed within; basal margin short, (only equalling half the length of terga), owing to the great curvature of the lower part of the carino-tergal margin; hence, the outline of the scuta is almost pointed oval. I saw no appearance of inequality in the two sides.

Terga, rather smaller in proportion to the scuta, than in P. Kæmpferi, with the basal end very obliquely truncated, so as to appear at first simply pointed, not parallel to the occludent margin; apex considerably more pointed and produced than in the foregoing species.

Carina, almost of equal narrowness throughout, barely concave within; lower end triangular, abruptly truncated, and not crested.

Primordial valves very plain, with the usual hexagonal structure: those of the terga, rounded at both ends, instead of being square, as in the mature calcified valves.

Peduncle short, narrow, not half as long as the capitulum; paved with minute equal beads, as in the genus Dichelaspis.

Mouth.—Mandibles with the fourth tooth very small; inferior angle rudimentary. Maxillæ, with three great upper spines, beneath which there is a deep notch bearing some delicate spines; inferior upraised part, as in P. Kæmpferi.

Cirri.—Rami of first cirrus hardly more than one third as long as the rami of the second cirrus, which latter rami are unequal in length by only two segments; the posterior ramus being the longer one.

Caudal Appendages, with only two or three lateral bristles, besides those on the summit.

Size.—Capitulum, three to four tenths of an inch long.

General Remarks.—This species has the closest general resemblance to P. Kæmpferi, and is evidently a representative of it. On close examination, however, almost every part differs slightly; the chief points being the narrowness of the basal margin of the scuta; the obliqueness of the truncated basal end of the terga and the sharpness of the upper end; the rudimentary state of the inferior angle of the mandibles; the character of the spines on the maxillæ; the proportional lengths of the cirri, and the fewness of the spines on the outer sides of the caudal appendages. The fact of Madeira having this Pæcilasma, a representative both in structure and habits of a Japan species, is interesting, inasmuch, as I am informed by Mr. Lowe, that some of the Madeira fishes are analogues of those of Japan.

3. Pæcilasma crassa. Pl. II, Fig. 3.

Anatifa crassa. J. E. Gray. Proc. Zoolog. Soc., 1848, p. 44, Annulosa, Tab. iii, figs. 5, 6.

P. valvis 5; carinæ termino basali in discum parvum infossum producto: scutis convexis, dentibus internis umbonalibus nullis: tergis pæne rudimentalibus, vix carinâ latioribus.

Valves 5; carina with the basal end produced into a small imbedded disc; scuta convex, without internal umbonal teeth; terga almost rudimentary, scarcely broader than the carina.

Spines on the segments of the posterior cirri arranged in single transverse rows.

Madeira; attached to the Homola Cuvierii, Rev. R. T. Lowe. British Museum.[31]

General Appearance.—Capitulum highly bullate, or thick. Valves rather thick, opaque, either pale or dark flesh-red, smooth, yet rather plainly striated from the umbones. There are a few very minute spines on the membranous borders of the valves.

Scuta highly convex, broadly oval, apex broad rounded; basal margin narrow, much curved; no internal, umbonal teeth; basal internal rim strong, running up part of the occludent margin. A slightly prominent ridge, either rounded or angular, but in one specimen a narrow depressed fissure-like line, runs parallel to the occludent margin and ends near the apex in a slight notch; this fact is of interest in relation to the structure of the scuta in P. eburnea and P. fissa. The scuta are either equally or very unequally convex; in the latter case, the occludent margin of one valve is curled, so that its umbo is not quite medial.

[31] It is stated, in 'Zoolog. Proc.,' (1848, p. 44,) that this species was attached to a gorgonia, from Madeira; I cannot but suspect that there has been some confusion with the Oxynaspis celata from Madeira, which is thus attached.

Terga, minute, almost rudimentary, scarcely broader than the carina, and half as long as the chord of its arc; carinal margin slightly curved; scutal margin straight, with a slight prominence fitting into a notch in the scuta; basal end bluntly pointed.

Carina, (fig. 3, a) rather shorter than the scuta, extending up only to the basal ends of the terga; moderately curved; apex moderately sharp; middle part broadest, externally carinated; internally not concave, with the inner lamina of shell, at the basal end, produced into a very small oblong disc or tooth, which is only as wide as the narrowest upper part of the valve. The exterior keel does not extend on to this disc, which is slightly constricted at its origin.

Peduncle very short, narrow, ringed, and apparently without spines.

Size.—Capitulum four tenths of an inch long.

The following parts of the animal are described from some small and not well preserved specimens from Madeira, which I owe to the kindness of Mr. Lowe.

Mouth.—Labrum highly bullate in the upper part, with large, inwardly pointed, unequal teeth. Mandibles, with four large, pointed, equal-sized teeth, with the inferior angle very narrow, acuminated like a single spine. Maxillæ, with three (?) large upper spines, of which the middle one is extremely strong and long, beneath which, there is a deep notch with a single strong spine, and with the whole inferior part square and much upraised, so as to stand on a level almost with the tips of the great upper spines.

Cirri in a miserable state of preservation; first cirrus short, second cirrus with rami unequal, and I suspect the anterior one the longest; some of the other cirri also have unequal rami. The segments of the posterior cirri are not protuberant, they have on their anterior faces a single transverse row of bristles: in the upper segments, some of the spines in each dorsal tuft (which is much spread out), are much thicker, though rather shorter than those on the anterior face. This peculiar structure is common to all five posterior cirri.

Caudal Appendages.—I can only say that they are spinose on their summits.

Affinities.—This species is allied to P. eburnea in the rudimentary condition of its terga; in the disc-shaped basal end of its carina; and in the presence in some specimens, of a fissure-like line on the scuta parallel to their occludent margins. Its affinity, however, is closer to P. fissa, as is more especially shown by the remarkable arrangement of the spines on the five posterior cirri.

4. Pæcilasma fissa. Pl. II, Fig. 4.

P. valvis 7; scuto utroque è duobus juxtapositis segmentis formato; segmento altero intus dentato: tergis brevibus, ter aut quater carinâ latioribus: carinæ termino basali in discum parvum angustum infossum producto.

Valves 7; each scutum being formed of two closely approximate segments; of which one is internally toothed: terga short, three or four times as wide as the carina: carina with the basal end produced into a small, narrow, imbedded disc.

Spines on the segments of the posterior cirri arranged in single transverse rows.

Philippine Archipelago; Island of Bohol; parasitic on a spinose crab, found under a stone at low water; single specimen, in Mus., Cuming.

General Appearance.—Capitulum gibbous, broadly oval, nearly a quarter of an inch long. Valves white, smooth, moderately thick, marked by the lines of growth. The occludent segments of the scuta, and nearly the whole of the terga, and the whole of the carina, enveloped in lemon-yellow membrane, tinged with orange, but the specimen had long been kept dry.

Scuta formed of two, apparently always separate, segments, closely united, so that externally their separation is hardly visible, and does not allow of movement; the fissure thus formed runs almost in the line connecting the umbo and apex, (where in most species a ridge extends,) but a little on the carinal side of it. The occludent segment is narrowly bow-shaped, pointed at both ends, with the upper end projecting slightly beyond the apex of the lateral segment, and with the occludent margin regularly curved from end to end. The lateral segment is large, of an oval shape, with a narrow strip cut off on one side. Primordial valves very plain at the umbones of the lateral segments, but none are visible on the occludent segments; and this makes me believe that these two pieces are normally parts of a single valve; having only one specimen of P. fissa, I was not able to make out quite certainly whether the two segments are continuously united at their umbones by a non-calcified portion of valve, as is certainly the case with Dichelaspis. The basal margin of the lateral segment is narrow, inflected, and blends with the carino-tergal margin; it has an internal, prominent, basal rim, and towards the occludent margin a large, prominent, internal tooth. This internal basal rim is not parallel to the outer basal margin, but rises to a point a little way up the occludent margin, in the same manner as in P. eburnea, but in a lesser degree; in this latter species the peduncle is internally almost cut off by the large disc of its carina; here, on the other hand, it is internally almost cut off by these rims and the two large teeth of the lateral segments of the scuta.

Terga sub-triangular, short, nearly half as broad as long; three or four times as wide as the carina, and rather wider than the occludent segment of the scuta; occludent margin single, arched; carinal margin slightly arched; basal angle bluntly pointed.

Carina very narrow, much arched, running up just between the basal ends of the terga; exterior ridge enveloped in membrane; heel blunt, prominent; internally, not concave, even slightly convex, produced at the lower end into a very narrow, short, imbedded disc, (or rather tooth,) which is itself a little curved downwards and blunt at the end.

Peduncle very narrow, about half as long as the capitulum; yellow, finely beaded, plainly ringed, without spines.

Mouth.—Labrum, with a row of minute teeth; palpi narrow. Mandibles with all the lower part narrow; of the four teeth, the second and third are narrow, the fourth is pectinated and placed very close to the inferior angle, which is produced into a long thin tooth. Maxillæ unknown.

Cirri.—First pair lost. The arrangement of the spines on all is most abnormal, Pl. X, fig. 29: dorsal tuft long, arranged in a transverse line and seated in a deep notch; in the sixth cirrus, the spines on the lower segments are fine, those on the upper segments are thick and claw-like, mingled with some fine spines; in the four anterior cirri the spines of the dorsal tufts are even thicker and more claw-like. On the anterior faces, also, of all the segments the spines form a single row; they are shorter than those composing the dorsal tuft; hence the spines on each segment are arranged in a circle, interrupted widely on the two sides: this arrangement is common to all five posterior cirri. Second cirrus, with the anterior ramus one third longer and thinner than the posterior ramus (this is the reverse of the usual arrangement); this longer ramus equals in length the sixth cirrus. Third cirrus, with the anterior ramus considerably longer than the posterior ramus; in the three posterior pair of cirri, also, the anterior rami are a little longer than the posterior: except in length, there is little difference of any kind between the five posterior pair of cirri. Pedicels of the cirri long; rami rather short; segments elongated, not protuberant.

Caudal Appendages nearly as long as the pedicels of the sixth cirrus, thickly clothed with very fine bristles, like a camel's-hair pencil brush.

Affinities.—In the structure of the carina, and more especially of the scuta, there is a strong affinity between the present and following species; for we shall immediately see that in P. eburnea there is evidence of the scuta being composed of two segments fused together; and the larger segment is furnished with an internal oblique, strong, basal rim. To this same species there is an evident affinity in the form of the mandibles and of the caudal appendages, and in the anterior rami of the cirri being longer than the posterior rami. Notwithstanding these points of affinity, I consider that P. fissa is more closely related in its whole organisation, as more particularly shown in the arrangement of the spines on the cirri and in the presence of terga, to P. crassa than to P. eburnea. Although in Dichelaspis, the scuta are invariably composed of two almost separate segments, yet P. fissa shows no special affinity to this genus.

5. Pæcilasma eburnea. Pl. II, Fig. 5.

Trilasmis eburnea. Hinds. Voyage of Sulphur, 1844, vol. i, Mollusca, Pl. xxi, fig. 5.

P. valvis 3; scutis acuminatis, ovatis; ad pedunculum pæne transversè spectantibus; dentibus internis umbonalibus fortibus: tergis nullis: carinæ termino basali in discum amplum oblongum infossum producto.

Valves 3; scuta pointed, oval, placed almost transversely to the peduncle; internal umbonal teeth strong: terga absent: carina with the basal end produced into a large, oblong, imbedded disc.

Spines on the upper segments of the posterior cirri, arranged in three or four approximate longitudinal rows, making small brushes.

Habitat.—New Guinea, attached to the spines of a dead Echinus. Brit. Mus., and Cuming.

General Appearance.—Capitulum flat, pear-shaped, placed almost transversely to the peduncle. Valves white, smooth, moderately thick.

Scuta: the basal margin, as seen externally, is narrow, and can hardly be separated from the carinal margin; but an internal basal rim, (fig. 5, b) (along which the imbedded disc of the carina runs,) shows where, in the other species, the basal and carinal margins are separated. This basal internal rim is not parallel to the external basal margin, but runs upwards to the occludent margin, leaving beneath it a large triangular space, to which the membrane of the peduncle is attached; and this makes it appear as if the rostral umbones of these valves had grown downwards; but, judging from the allied species, P. fissa, I have no doubt that the primordial valves really lie on the umbones, and that the growth has been in the usual direction, that is, exclusively upwards. The occludent margin is curved, and blends by a regular sweep into the carinal margin, so that there is no acute upper angle. A distinct line can be seen, as if two calcareous valves had been united, running from the umbo to the upper end of the valve, thus in appearance separating a slip of the occludent margin; internally this appearance is more conspicuous; this structure is important in relation to that of P. fissa. The pointed umbones are divergent, and internally under each, there is a large tooth. The two valves are equally convex.

Terga, entirely absent.

The Carina (Tab. II, fig. 5, a, c), including the disc, is three fourths as long as the scuta; it is placed almost transversely to the longitudinal axis of the peduncle; it is narrow and internally convex; the imbedded disc is very large, forming a continuous curve with the upper part of the carina; this disc runs along the internal basal rim of the scuta, and hence almost separates, internally, the peduncle from the capitulum; it equals one fourth of the total length of the valve, and is thrice as wide as the upper part; it is oval, externally marked by a central line, and with a slight notch at the end, giving a divided appearance to the whole, and indicating how easily a fork might be formed from it. The carina is thick, measured from the inner convex to the exterior surface, which is carinated; heel prominent.

Peduncle, narrow, very short, not nearly so long as the capitulum.

Mouth.—Labrum considerably bullate, with the lower part much produced towards the adductor muscle; crest with small bead-like teeth; palpi small, pointed; mandibles, with the first tooth standing rather distant from the second; inferior angle spine-like and bifid; maxillæ (Pl. X, fig. 15), with two considerable spines (only one is shown in the Plate) beneath the upper large pair; the inferior upraised part bears seven or eight pair of spines, and its edge is not quite straight; close to the main notch, lying under the four upper spines, there are two minute notches, with the interspace bearing a tuft of fine spines and a pair of larger ones.

Cirri.—The rami in all are rather unequal in length, the anterior rami being rather the longest; the anterior rami of the second and third cirri are not thicker than the posterior rami. The segments in the three posterior cirri are not protuberant; the upper segments bear three or four pair of spines, with some minute intermediate ones, and with the lateral marginal spines unusually large and long, so as to form, with the ordinary pairs, a third or fourth longitudinal row; hence a small brush is formed on each segment. The dorsal tuft is large and wide, so as to contain even fourteen spines, of which some are as long as those in front. In the lower segments of these same posterior cirri, the lateral marginal spines are not so much developed (nor is the dorsal tuft), and hence the segments can hardly be said to be brush-like. The first cirrus is placed rather distant from the second pair. The second and third cirri differ from the three posterior pair, only in the bristles being slightly more numerous, and in the dorsal tufts being more spread out.

Caudal Appendages about half the length of the lower segments of the pedicels of the sixth cirrus; truncated and rounded at their ends; thickly clothed with long excessively fine bristles, so as to resemble camel-hair pencils.

The Stomach, I believe, is destitute of cæca; in it was a small crustacean.

General Remarks.—I was at first unwilling to sacrifice Mr. Hind's genus, Trilasmis, which is so neatly characterised by its three valves; moreover, the present species does differ, in some slight respects, from the other species of Pæcilasma; but under the head of P. fissa I have shown how that species, P. crassa and P. eburnea are tied together. The absence of terga, which are rudimentary in P. crassa, (and we shall hereafter see, in Conchoderma, how worthless a character their entire absence is,) and the arrangement of the spines in the upper segments of the posterior cirri, are the only characters which could be used for a generic separation.

Genus—Dichelaspis. Plate II.

Octolasmis.[32] J. E. Gray. Annals of Philosophy, vol. x, new series, p. 100, August 1825.

Heptalasmis. Agassiz. Nomenclator Zoologicus.

Valvæ 5, quæ ferè pro septem haberi possent, scuto in segmenta planè duo, ad angulum autem rostralem conjuncta, diviso: carina plerumque sursum inter terga extensa, deorsum aut disco infosso aut furcâ aut calyce terminata.

[32] From [Greek: dichêlos], bifid, and [Greek: aspis], a shield, or scutum. The name Octolasmis was given by Mr. Gray under the belief that there were eight valves. Leach (as stated in the 'Annals of Philosophy,') had proposed, in MS., the name Heptalasmis, and this is now used in the British Museum by Mr. Gray, and thus appears in Agassiz's 'Nomenclator Zoologicus.' Although, strictly, there are only five valves, I continued to use, in my MS., the term Heptalasmis, until I examined the D. orthogonia, where it was so apparent to the naked eye that there were only five valves, the scuta in this species being less deeply bifid, that I was compelled to give up a name so manifestly conveying a wrong impression, and hence adopted the one here used.

Valves 5, generally appearing like 7, from each scutum being divided into two distinct segments, united at the rostral angle; carina generally extending up between the terga terminating downwards in an imbedded disc, or fork, or cup.

Mandibles, with three or four teeth; maxillæ notched, with the lower part of edge generally not prominent; anterior ramus of the second cirrus not thicker than the posterior ramus, not very thickly clothed with spines; caudal appendages uniarticulate, spinose.

Distribution.—Eastern and Western warmer oceans in the Northern hemisphere, attached to crustacea, sea-snakes, &c.

Description.—The capitulum appears to contain seven valves; but, on examination, it is found that two of the valves on each side, are merely segments of the scutum; these are united at the umbo, in three of the species, by a narrow, non-calcified portion of valve, where the primordial valve is situated; in D. orthogonia, however, the junction of the two segments is perfectly calcified, and of the same width as the whole of the basal segment. The capitulum is much compressed, broad at the base, and extends a little beneath the basal segments of the scuta. The valves are very thin, often imperfectly calcified, and generally covered with membrane. They are not placed very close together, and in all the species a considerable interspace is left between the carina and the two other valves: in the D. Grayii the valves are so narrow that they form merely a calcified border round the capitulum. The membrane between the valves and over them, is very thin, and is thickly studded, in some of the species, with minute blunt conical points, apparently representing spines. The valves in the same species present considerable variations in shape; in their manner or direction of growth, and in the position of their primordial valves, they agree with Lepas and Pæcilasma.

Scuta.—In three of the species the two segments, named the occludent and basal, appear like separate valves, but these, by dissection, can be most distinctly seen to be united at the rostral angle. The primordial valve, formed of the usual hexagonal tissue, is elliptic, elongated, and placed in the direction of the occludent segment; calcification commences at its upper point, so as to form the occludent segment, and afterwards at its lower point, but rectangularly outwards, to form the basal segment; in the minute space between these two points of the primordial valve, there is, in four of the species, no calcification; so that the two segments are united by what may be called a flexible hinge; in D. orthogonia the two calcareous segments are absolutely continuous. The occludent segment is longer than the basal segment; it either runs close along the orifice, or in the upper part bends inwards; both segments are narrow, except in D. Warwickii, in which the basal segment is moderately broad; the two segments are placed at an angle, varying from 45° to 90°, to each other. The capitulum generally extends for a little space beneath the basal segments of the scuta, where it contracts to form the peduncle.

The Terga present singular differences in shape, and are described under the head of each species; scarcely any point can be predicated of them in common, except that they are flat and thin.

The Carina is much bowed, narrow, and internally either slightly concave or convex and solid; the upper end extends far up between the terga; the lower end is formed by a rectangularly inflected, imbedded, triangular or oblong disc, deeply notched at the end, or as in H. Lowei, of a fork, the base, however, of which is wider than the rest of the carina, so as to present some traces of the disc-like structure of the other two species; or lastly, as in D. orthogonia, it terminates in a crescent-formed cup.

Peduncle.—This is narrow, compressed, and about as long, or twice as long, as the capitulum; in D. Warwickii it is studded with minute beads of yellowish chitine.

Size.—Small, with a capitulum scarcely exceeding a quarter of a inch in length.

Filamentary Appendages.—None. There are two small ovigerous fræna, which, in D. Warwickii, had the glands collected in seven or eight little groups on their margins.

Mouth.—Labrum highly bullate, with small teeth on the crest; palpi small, not thickly covered with spines. Mandibles narrow, with three or four teeth. Maxillæ small, with a notch beneath the two or three great upper spines; lower part bearing only a few pair of spines, generally not projecting, but in D. orthogonia largely projecting. Outer maxillæ, with their inner edges continuously covered with bristles.

Cirri.—First pair short, situated rather far from the second pair; second pair with the anterior ramus not thicker than the posterior ramus, and hardly more thickly clothed with spines than it, excepting sometimes the few basal segments. All the five posterior pair of cirri resemble each other more closely than is usual. In D. Lowei, the segments of the posterior cirri bear the unusual number of eight pair of main spines.

Caudal Appendages.—Uni-articulate, spinose; in D. pellucida they are twice as long as the pedicels of the sixth cirrus, but I could not perceive in them any distinct articulations.

Distribution.—Attached to crabs at Madeira, and off Borneo; to sea-snakes in the Indian Ocean. The individuals of all the species appear to be rare.

General Remarks.—Four of the five species, forming this genus, though certainly distinct, are closely allied. I have already shown, that although the characters separating Lepas, Pæcilasma, and Dichelaspis are not very important, yet if they be neglected these three natural little groups must be confounded together. Dichelaspis is much more closely united to Pæcilasma than to Lepas, and, as far as the more important characters of the animal's body are concerned, there is no important difference between them. Consequently, I at first united Pæcilasma and Dichelaspis, but the latter forms so natural a genus, and is so easily distinguished externally, that I have thought it a pity to sacrifice it. The carina, (which seems to afford better characters than the other valves in Dichelaspis,) from generally running up between the terga and in ending downwards, in three of the species, in a deeply notched disc or fork, more resembles that in Lepas than in Pæcilasma; in the manner, however, in which the imbedded disc, in D. Warwickii and D. Grayii, nearly cuts off the inside of the capitulum from the peduncle, there is a resemblance to Pæcilasma eburnea. In the extent to which the valves are separated from each other, in the bilobed form of the scuta, (the two segments in Dichelaspis, perhaps, answering to the upper and lateral projections in the scuta of Conchoderma virgata,) and in the basal half of the scuta not descending to the base of the capitulum, there is a considerable resemblance to Conchoderma; in both genera the adductor muscle is attached under the umbones of the scuta; but the structure of the mouth and cirri and caudal appendages shows that the affinity is not stronger to Conchoderma than to Lepas. It appears at first probable, that Dichelaspis would present a much closer affinity to Pæcilasma fissa, in which, owing to the scuta being formed of two segments, there are seven valves, than to any other species of that genus; but in P. fissa the primordial valve is triangular and is situated on the basal segment, whereas, in Dichelaspis, it is elliptic and is seated between the two segments, and is more in connection with the occludent than with the basal segment; and this I cannot but think is an important difference: in other respects, P. fissa shows no more affinity to Dichelaspis than do the other species of the genus. Finally, I may add that Dichelaspis bears nearly the same relation to Pæcilasma, as Conchoderma does to Lepas.

1. Dichelaspis Warwickii. Pl. II, figs. 6, 6 a, b.

Octolasmis Warwickii. J. E. Gray. Annals of Philosophy, vol. x, p. 100, 1825; Spicilegia Zoologica. t. vi, fig. 16, 1830.

D. scutorum segmento basali duplo latiore quam segmentum occludens: tergorum parte inferiore paulò latiore quam occludens scutorum segmentum.

Scuta, with the basal segment twice as wide as the occludent segment; terga, with the lower part slightly wider than the occludent segment of the scuta.

Mandibles, generally with four teeth.

Off Borneo, attached to a crab (Belcher): China Sea. British Museum.

General Appearance.—Capitulum much compressed, elongated, with the valves not very close together, the carina being separated by a rather wide space from the scuta and terga. Valves variable in shape, very thin and translucent, covered by thin membrane, which, over the whole capitulum, is studded with minute blunt points.

Scuta.—Segments without internal teeth or an internal basal rim; the occludent segment long, narrow, pointed, not quite flat, sometimes slightly wider in the upper part; about one third of its own length longer than the basal segment; occludent margin slightly arched; basal segment about twice as wide as the occludent segment, triangular, slightly convex; in young specimens (Pl. II, fig. 6 b), the carinal margin of the basal segment is protuberant, and the occludent margin hollowed out; in old specimens the occludent margin of the basal segment is straight, and the carinal margin much hollowed out. In very young specimens the basal segment is very small compared to the occludent.

Terga, variable in shape; flat, lower part wider than the occludent segment of the scuta; occludent margin double, forming a considerable rectangular projection, as in the terga of Lepas; scutal margin deeply excised at a point corresponding with the apex of the scuta, a flat tooth or projection being thus formed; there is sometimes a second tooth (fig. 6 b) a little above the basal point. The terga, in the first variety, somewhat resemble in shape the scuta of Conchoderma aurita.

Carina, much bowed, narrow, slightly concave within, (in the Borneo specimen, rather wider and more concave,) extending up between the terga for half their length, terminating downwards in a rectangularly inflected, deeply imbedded, oblong, rather wide, flat disc, at its extremity more or less deeply notched. This disc is externally smooth; internally it sometimes has two divergent ridges on it; it extends across about two-thirds of the base of the capitulum (fig. 6 a, as seen from beneath, when the peduncle is cut off), to under the middle of the basal segments of the scuta.

Peduncle, narrow, flattened; united to the capitulum some little way below the scuta; about as long as the capitulum; the membrane of which it is composed is thin, externally studded with bluntly conical beads of yellowish chitine, of which the largest were 1/2000 of an inch in diameter; on their internal surfaces these are furnished with a small central, circular depression, apparently for a tubulus; the arrangement of the beads varied in concentric zones. Similar conical points on the capitulum have an internal concave surface about 1/3000 in diameter, with a central circle 1/12000 in diameter, for the insertion, as I believe, of a tubulus.

Size.—The largest specimen had a capitulum a quarter of an inch long.

Mouth.—Labrum highly bullate; crest with not very minute, blunt teeth, which towards the middle lie closer and closer to each other, so as to touch. Palpi rather small, with a few very long bristles at the apex.

Mandibles, narrow, produced, with four teeth, and the inferior angle tooth-like and acuminated; in one specimen, on one side of the mouth, the mandible had only three teeth.

Maxillæ, small; at the upper angle there are two large spines and a single small one, beneath which there is a deep notch, and beneath this a straight but projecting edge, bearing a few moderately large and some smaller spines. Outer maxillæ sparingly covered with bristles along the inner margin.

Cirri.—First pair far removed from the second pair, and not above half their length; segments rather broad, with transverse rows of bristles not very thickly crowded together; terminal segments very obtuse, and furnished with thick spines. The segments of the three posterior pair have each three or four pair of spines, with a few minute spines scattered in an exterior, parallel, longitudinal row; dorsal tufts, with four or five long spines. The second cirrus has its anterior ramus not thicker, but rather shorter than the posterior ramus; the former is only a little more thickly clothed with spines, owing to those in the longitudinal lateral row being longer and more numerous, than is the sixth pair of cirri. Bristles not serrated.

Caudal Appendages, narrow, thin, slightly curved, about half as long as the pedicels of the sixth cirrus; in young specimens, the appendage bore seven or eight pair of long bristles rectangularly projecting; in some older specimens, there was a tuft of bristles on the summit, and two other tufts on the sides.

I at first thought that the Borneo specimen was a distinct species, but after careful comparison of the external and internal parts, the only difference which I can detect is, that the terga are slightly larger, and that the carina, to a more evident degree, is wider, more especially in the middle and lower portions.

2. Dichelaspis Grayii. Pl. II, fig. 9.

D. scutorum segmento basali angustiore quam segmentum occludens; longitudine pæne dimidiâ: tergis bipenniformibus, margine crenato, spinâ posticâ, manubrio angustiore quam occludens scutorum segmentum.

Scuta, with the basal segment narrower than the occludent segment, and about half as long as it. Terga like a battle-axe, with the edge crenated and a spike behind; the handle narrower than the occludent segment of the scuta.

Mandibles with three teeth; cirri unknown.

Attached to the skin of a sea-snake, believed to have been the Hydeus or Pelamis bicolor, and therefore from the Tropical, Indian or Pacific Oceans; associated with the Conchoderma Hunteri; single specimen, in a very bad condition, in the Royal College of Surgeons.

General Appearance.—Capitulum much compressed, elongated, formed of very thin membrane, with the valves forming round it a mere border. Valves thin, imperfectly calcified, covered with membrane.

Scuta formed of two narrow plates at very nearly right-angles to each other, one extending along the occludent, and the other along the basal margin; both become very narrow at the point of junction, and are there not calcified, but are evidently continuous and form part of the same valve; the basal segment is about half as long and narrower than the occludent segment, flat and bluntly pointed at the end; occludent segment slightly curled, and therefore the whole does not lie quite in the same plane; narrow close to the umbo, with a very minute tooth on the under side; apex rounded. In the upper part, the occludent segments leave the membranous margin of the orifice, and run in near to the terga, bending towards them at an angle of 45° with their lower part. I was unable to distinguish the primordial valves.

Terga.—These valves are of the most singular shape, resembling a battle-axe, with a flat and rather broad handle; the upper part consists of an axe, with a broad cutting crenated edge, behind which is a short blunt spike. The spike and cutting edge together answer to the double occludent margin of the tergum in Lepas. The whole valve is flat, thin, and lies in the same plane; the carinal margin is nearly straight; the scutal margin bulges out a little, and at a short distance above the blunt basal point is suddenly narrowed in, making the lowermost portion very narrow; the widest part of the handle of the battle-axe, is narrower than the occludent segment of the scuta. The two spikes behind the cutting and crenated edges of the two terga, are blunt and almost touch each other; above their point of juncture, the membrane of the orifice forms a slight central protuberance.

Carina, very narrow throughout, concave within, much bowed; upper point broken and lost, but it must have run up between the terga for more than half their length; basal portion inflected at nearly right angles, and running in between, and close below, the linear basal segments of the scuta, so as almost entirely to cut off internally the peduncle and capitulum. This lower inflected and imbedded portion, or disc, gradually widens towards its further end, which is, at least, four times as wide as the upper part of the carina, and is deeply excised, but to what exact extent I cannot state, as the specimen was much broken. On each side of this elongated triangular disc, there is a slight shoulder corresponding to the ends of the basal segments of the scuta; and on the upper surface of each shoulder, there is a small tooth or projection. The middle part of the disc is barely calcified, and is transparent.

Peduncle, rather longer than, and not above half as wide as, the capitulum; the latter being nearly 2/10ths of an inch in length: the membrane of the peduncle is thin, naked and structureless.

Mouth.—Labrum highly protuberant in the upper part, with a row of beads on the crest. Palpi small, with few bristles. Mandibles, with the whole inferior part, very narrow; three teeth very sharp, with a slight projection, perhaps, marking the place of a fourth tooth; inferior angle ending in the minutest point; first tooth as far from the second, as the latter from the inferior angle. Maxillæ with a broad shallow notch; inferior angle much rounded, bearing only four or five pair of spines.

Cirri.—First pair apparently remote from the second pair; all five posterior pair lost; first pair short, with the rami unequal by about two segments; segments clothed with several transverse rows of bristles; terminal segments blunt.

3. Dichelaspis pellucida. Pl. II, fig. 7.

D. valvarum singularum acuminibus superioribus et inferioribus vix intersecantibus: scutorum segmento basali multo angustiore quam segmentum occludens; longitudine ferè dimidiâ: tergis bipenniformibus, margine integro, manubrii acumine ad carinam flexo.

Valves with the upper and lower points of the several valves only just crossing each other. Scuta with the basal segment much narrower than the occludent segment, and about half as long as it. Terga like a battle-axe, with the edge smooth, and the point of the handle bent towards the carina.

Mandibles with four teeth; caudal appendages twice as long as the pedicels of the sixth cirrus.

Indian Ocean; attached to a sea-snake.

This species comes very close to the D. Grayii, which likewise was attached to a snake; but I cannot persuade myself, without seeing a graduated series, that the differences immediately to be pointed out can be due to ordinary variation. I am much indebted for specimens to the kindness of Mr. Busk.

General Appearance.—The membrane of the capitulum and peduncle is surprisingly thin and pellucid, so that the ovarian tubes within the peduncle can be traced with the greatest ease. The valves are small, the apices only just crossing each other, and are composed of yellow chitine, with mere traces of calcification. The capitulum is pointed, oval, .15 of an inch long; the peduncle is narrow, and fully twice as long as the capitulum.

Scuta.—The two segments stand at right-angles to each other; the basal segment is linear and pointed, fully half as long, but only one third as wide, as the occludent segment. The point of junction of the two segments is wider than the rest of the basal segment. This latter segment lies some little way above the top of the peduncle. The occludent segment is bluntly pointed; it is directed a little inwards from the edge of the orifice towards the terga; the apex reaches up just above the slightly reflexed lower point of the terga. The adductor muscle is fixed under the point of junction of the two segments.

The Terga are battle axe-shaped, with the blade part very prominent, smooth-edged; behind the blade there is a short upwardly-turned prominence. The lower point of the handle of the axe, is bent towards the carina. The tergum, measured in a straight line, equals in length two thirds of the occludent segment of the scutum, the handle being rather narrower than this same segment.

The Carina is extremely narrow and much bowed; the apex reaches up only to just above the lower bent points of the terga. The basal end is rectangularly inflected, and stretches internally nearly across the peduncle; it consists (fig. 7 a) of a triangular disc of yellow thin membrane, four or five times as wide as the upper part of the valve; the end of this disc is hollowed out; its edges are thickened and calcified, and hence, at first, instead of a disc, this lower part of the carina appears like a wide fork; the tips of the prongs stretch just under the tips of the basal segments of the scuta.

Peduncle.—Its narrowness and transparency are its only two remarkable characters.

Mouth.—All the parts closely resemble those of D. Grayii, but being in a better state of preservation I will describe them. The labrum is highly bullate, with a row of minute teeth on the crest, placed very close together in the middle. Palpi small, thinly clothed with spines; mandibles extremely narrow, hairy, with four teeth, but the lower tooth is so close to the inferior angle, as only to make the latter look double. Maxillæ, with a very deep broad notch, dividing the whole into two almost equal halves; in the upper part there are three main spines.

Cirri.—The first pair are placed at a considerable distance from the second pair; they are short with equal rami, and rather broad segments furnished with a few transverse rows of bristles. The five posterior cirri have singularly few, but much elongated segments, bearing four pair of spines: the two rami of the second pair are alike, and differ only from the posterior cirri in a few of the basal segments having a few more spines.

The Caudal Appendages are twice as long as the pedicels, and nearly half as long as the whole of the sixth cirrus; they have a small tuft of long thin spines at their ends, and a few in pairs, or single, along their whole length; at first I thought that they were multi-articulate, but after careful examination I can perceive no distinct articulations; I have seen no other instance of so long an appendage without articulations.

Diagnosis.—This species differs from D. Grayii in all the valves being shorter, so that their points only just cross each other; but this, I conceive, is an unimportant character. In the scuta, the basal segment is here narrower, but the point of junction of the two segments wider than in that species; in the terga, the edge of the axe is smooth instead of being crenated, and the handle and the point behind are of a rather different shape; in the carina the imbedded basal disc has not shoulders and small teeth, as in D. Grayii. Notwithstanding these differences, I should not be much surprised if the present form were to turn out to be a mere variety.

4. Dichelaspis Lowei. Pl. II, fig. 8.

D. scutorum segmento basali angustiore quam occludens segmentum, longitudine ferè 4/5: tergorum parte inferiori duplo latiore quam occludens scutorum segmentum.

Scuta with the basal segment narrower than the occludent segment, and about four-fifths as long as it. Terga with the lower part twice as wide as the occludent segment of the scuta.

Mandibles with four teeth; segments of the three posterior cirri with eight pair of main spines.

Hab.—Madeira; attached to a rare Brachyourous Crab, discovered by the Rev R. T. Lowe. Very rare.

General Appearance.—Capitulum much compressed, sub-triangular, formed of very thin membrane; valves imperfectly calcified, and thin.

Scuta formed of two narrow plates placed at about an angle of 50° to each other, and united at the umbo by a non-calcified flexible portion. The primordial valve is situated at this point, but chiefly on the occludent segment. The occludent segment is about twice as wide and about one fifth longer than the basal segment, which latter is rather sharply pointed at its end. The occludent segment is slightly arched, a little narrowed in on the occludent margin close to the umbo; its upper end is broad and blunt; it runs throughout close to the edge of the orifice of the sack, and its longer axis is in the same line with that of the terga. Close to the umbones, on the under side of the basal segment, there is, on each valve, a longitudinal calcified fold, serving as a tooth.

Terga broad, with a deep notch corresponding to the apex of the occludent segment of the scuta; the part beneath the notch is of nearly the same width throughout, and is twice as broad as the occludent segment of the scuta; it has its basal angle very broad and blunt. The entire length of the terga equals two thirds of that of the occludent segment of the scuta; occludent margin simply and slightly curved.

The Carina is of nearly the same width throughout, with the upper part rather the widest, and the apex blunt; within convex; it extends up between three fourths of the length of the terga, terminating downwards in a fork with very sharp prongs, standing at right-angles to each other (fig. 8 a.) The fork, measured from point to point, is thrice as wide as, and measured across at the bottom of the prongs it is wider than, the widest upper part of the valve,—a resemblance being thus shown with the triangular notched disc in D. Grayii. The points of the prong extend under about one fourth of the length of the basal segments of the scuta.

Peduncle rather longer than the capitulum, which, in the largest specimen, was 2/10ths of an inch in length; peduncle narrow, close under the capitulum; membrane thin and structureless. The larger specimen had almost mature ova in the lamellæ.

Mouth.—Labrum with a few bead-like teeth on the crest, distant from each other even in the central part; palpi rather small, moderately clothed with bristles.

Mandibles, with four teeth; the inferior angle blunt and broad, showing, apparently, a rudiment of a fifth tooth; the first tooth is as far from the second, as is this from the inferior angle; second, third, and fourth teeth very blunt, whole inferior part of mandible not much narrowed. Maxillæ small, with a small notch under the three upper spines, which are followed by five or six pair, nearly as large as the upper spines.

Cirri.—First pair remote from the second; their rami nearly equal, and about one third of the length of the rami of the second cirrus; thickly clothed with bristles: rami of the second cirrus of equal thickness, but little shorter than those of the sixth cirrus; the three or four basal segments of the anterior ramus are thickly clothed with spines; the other segments, and all the segments on the third pair, resemble the segments of the three posterior pair. These latter are elongated, not protuberant, and support eight pairs of spines with very minute intermediate spines; those in the dorsal tufts are numerous and long.

Caudal Appendages nearly as long as the pedicels of the sixth cirrus; oval, moderately pointed, with their sides, for one fourth of their length, thickly clothed with long very thin spines.

Affinities.—In the form of the scuta and of the carina this species is most nearly allied to D. Grayii or D. pellucida, in the form of the terga to D. Warwickii.

5. Dichelaspis orthogonia. Pl. II, fig. 10.

D. scutorum basali segmento angustiore quam occludens segmentum; longitudine ferè dimidiâ; duorum segmentorum junctione calcareâ: tergorum prominentiis marginalibus inæqualibus quinque: carinâ deorsum in parvo calyce lunato terminatâ.

Scuta with the basal segment narrower than the occludent segment, and about half as long as it; junction of the two segments calcified. Terga with five unequal marginal projections. Carina terminating downwards in a small crescent-formed cup.

Maxillæ with the inferior part of edge much upraised.

Hab. unknown; associated with Scalpellum rutilum, apparently attached to a horny coralline. British Museum.

The specimens are in a bad condition, not one with all the valves in their proper positions, and most of them broken; animal's body much decayed and fragile.

General Appearance.—Capitulum apparently much flattened; valves naked, coloured reddish, separated from each other by thin structureless membrane.

The Scuta consist of two bars placed at right-angles to each other, with the point of junction fully as wide as any part of the basal segment, and perfectly calcified; the primordial valve lies at the bottom of the occludent segment. The basal segment is equally narrow throughout, and very slightly concave within; the occludent segment widens a little above the junction or umbo, and then keeps of the same width to the apex, which is obliquely truncated; internally this segment is concave; externally it has a central ridge running along it; the occludent segment is twice as long and twice as broad as the basal segment. Both segments are a little bowed from their junction to their apices.

Terga.—These are of a singular shape; they are about three-fourths as long as the occludent segment of the scuta, and in their widest part, of greater width than it. They consist of four prominent ridges proceeding from the umbo, and united together for part only of their length, and, therefore, ending in four prominences; one of these, the longest, has the same width throughout, and forms the basal point; a second, very small one, is seated high up on the carinal margin just above the apex of the carina; the third and fourth, are nearly equal in length, and project one above the other on the scutal margin. There are two occludent margins, meeting each other at right angles, and forming a prominence, as in Lepas; and this gives to the margin of the valve the five prominences. The whole valve internally is flat; externally, it is ridged as described.

Carina (fig. 10, a, b), much bowed, narrow, long; externally, the central ridge is quite flattened; internally, slightly concave, but scarcely so towards the lower part, which is narrow; the upper part widens gradually, and the apex is rounded. The basal embedded portion is as wide as the uppermost part, and forms a cup, unlike anything else known: the outline of this cup is semi-oval and crescent-formed; it is moderately deep; it is formed by the external lamina of the carina bending rectangularly downwards and a little outwards, whereas the inner lamina of the lower part (which is slightly concave), is continued with the same curve as just above, and forms the concave chord to the semi-oval rim of the cup. This cup, I believe, lies under the points of the basal segments of the scuta.

Peduncle unknown, probably short.

Length of capitulum, above 2/10ths of an inch.

Mouth.—Labrum with the upper part highly bullate, and produced into a large overhanging projection; crest with a row of rather large bead-like teeth; palpi small, their two sides parallel, very sparingly covered with long bristles.

Mandibles, narrow, produced, with four teeth, and the inferior angle produced into a single strong spine: the distance between the tips of the first and second teeth almost equals that between the tip of the second tooth and of the inferior angle.

Maxillæ with three large upper unequal spines, beneath which, there is a deep and wide notch (bearing one spine), and the inferior part projects highly, bearing three or four pairs of spines, and is, itself, obscurely divided into two steps.

Outer Maxillæ, very sparingly covered with bristles; outline, hemispherical.

Cirri.—The rami of the five posterior pair are extremely long, as are the pedicels; the segments are much elongated, with their anterior faces not at all protuberant; each bears five pair of very long and thin spines, with an excessively minute one between each pair; the dorsal tuft consists of very fine and thin spines. The second cirrus has its anterior ramus not at all thicker than the posterior ramus; but has an exterior third longitudinal row of small bristles. First cirrus, separated by a wide interval from the second pair; very short with the two rami slightly unequal in length; the segments are broad, and are paved moderately thickly with spines; the terminal spines not particularly thick.

Caudal Appendages consist of very small and narrow plates, about half the length of the pedicels of the sixth cirrus, with a few long spines at their ends.

This well-marked species, I think, has not more affinity to one than to another of the previous species: it differs from all, in the junction between the two segments of the scuta being perfectly calcified; in the peculiar cup, forming the base of the carina; and lastly, in the inferior part of the maxillæ projecting.

Oxynaspis.[33] Gen. Nov. Pl. III.

Valvæ 5, approximatæ: scutorum umbones in medio marginis occludentis positi: carina rectangulè flexa, sursùm inter terga extensa, termino basali simpliciter concavo.

Valves 5, approximate; scuta with their umbones in the middle of the occludent margin; carina rectangularly bent, extending up between the terga, with the basal end simply concave.

[33] From

οξυνω

, to sharpen, and

ασπις

, a shield or scutum.

Mandibles with four teeth; maxillæ notched, with the lower part of edge nearly straight, prominent; anterior ramus of the second cirrus thicker than the posterior ramus; caudal appendages, uniarticulate, spinose.

Attached to horny corallines.

I have most unwillingly instituted this genus; but it will be seen by the following description, that the one known species could not have been introduced into Lepas or Pæcilasma, without destroying these genera, although it has a close general resemblance with both. As far as the valves are concerned, it is more nearly related to Lepas than to Pæcilasma; but taking the entire animal, its relation is much closer to the latter genus than to Lepas: it differs from both these genera in the manner of growth of the scuta, which is both upwards and downwards, the primordial valve being situated in nearly the middle of the occludent margin. In this respect, and in the shape of the carina and terga, there is an almost absolute identity with Scalpellum; I may, however, remark that in Scalpellum, the scuta first grow downwards, and afterwards in most of the species upwards, whereas here from the beginning, the growth is both upwards and downwards. In the mouth and cirri, there is rather more resemblance to Scalpellum than to Pæcilasma and Lepas: in habits, also, this genus agrees with Scalpellum, and if it had possessed a lower whorl of valves, it would have quite naturally entered that genus. It is unfortunate, that so insignificant and poorly characterised a form should require a generic appellation. In natural position, it appears to lead from Scalpellum through Pæcilasma to Lepas.

1. Oxynaspis celata. Pl. III, fig. 1.

Madeira; attached in numbers to an Antipathes; Rev. R. T. Lowe. Mus., Hancock.

General Appearance.—The capitulum is rather thin, and broad in proportion to its length; it seems always entirely covered by the horny muricated bark of the Antipathes, and hence externally is coloured rich brown and covered with little horny spines. The membrane over the valves is very thin, and is with difficulty separated from the Antipathes; it has, I believe, no spines of its own. The corium lining the peduncle is a fine purple. All the individuals are attached to the coralline, with their capitulums upwards in the direction of the branches, and in this respect fig. 1. is erroneous.

The valves, when cleared of the bark, are white, or are strongly tinged with pinkish-orange. The upper parts of the scuta and terga are plainly furrowed in lines radiating from their umbones; hence their margins are serrated with blunt teeth; their surfaces, moreover, are sparingly studded with small calcareous points.

Scuta (fig. 1, a), sub-triangular, with the lower part rounded and protuberant, the upper produced and pointed. The umbo is situated in the middle of the occludent margin, instead of at the rostral angle, as in the foregoing genera. The occludent margin is straight, and is bordered by a narrow step or ledge, formed of transverse growth-ridges, and therefore has its edge serrated: the rostral angle is often slightly produced into a small projection. The basal margin is short, and forms an angle above a rectangle with the occludent margin: the tergal margin is straight; the carinal margin is rounded, protuberant, and of unusual length compared to the basal margin. The surface of the valve is convex near the umbo; and beneath there is a large deep hollow for the adductor muscle.

Terga (fig. 1, b) large, flat, triangular, as long as the scuta or the carina, all three valves being nearly equal in length; occludent margin straight, or slightly arched, basal angle broad, not very sharp.

Carina short (fig. 1, c, drawn rather too long), deeply concave, rectangularly bent, with the lower part not quite as long as the upper, and a little wider: the basal margin is truncated, rounded, and slightly sinuous. The umbo is situated at the angle, and therefore nearly central. The umbo of the terga, I may add, is in the same place, as in Lepas.

The peduncle is very short and narrow, and is, I believe, without spines; it is enveloped by the bark of the Antipathes. The capitulum in the largest specimens was .2 of an inch in length.

Filamentary Appendages, apparently none.

Mouth, with the orifice rather inclined abdominally.

Labrum, with the upper part extremely protuberant, forming a projecting horn; no teeth on the crest. Palpi rather small, with only a few bristles at the end.

Mandibles, with four teeth and the inferior angle pointed: first tooth as far from the second, as is the latter from the inferior angle; in one specimen, on one side, there were five teeth.

Maxillæ with three great spines at the upper angle, beneath which a deep notch, and with the inferior part much upraised; this lower part rather rounded at both corners, with the upper spines longer than the lower.

Outer Maxillæ, with the bristles continuous in front; externally, slightly protuberant, with a tuft of bristles longer than those on the front side. Olfactory orifices apparently not protuberant; but all the specimens were in a bad state.

Cirri.—Prosoma very little developed. First cirrus very far removed from the second. The three posterior cirri are straight and long; the segments are elongated and bear four or five pairs of very long spines, with a single minute intermediate spine between each pair; dorsal tufts, with long spines. First cirrus, rami unequal by two or three segments, and thickly covered with spines; the first cirrus is short compared to the second, owing to the length of the pedicel of the latter, though the longer ramus of the first, nearly equals the shorter ramus of the second pair. Second cirrus, with its anterior ramus shorter by two or three segments than the posterior ramus, and thicker than it, with the segments covered like brushes with bristles; posterior ramus, and both rami of the third cirrus, a little more thickly clothed with bristles than are the three posterior cirri.

Caudal Appendages, minute, broadly oval, with six or seven long bristles on their summits.

Genus—Conchoderma. Plate III.

Conchoderma. Olfers. Magaz. der Gesellsch.

Natuforsch.

Freunde zu Berlin, Drittes Quartel, 1814.[34]

Lepas. Linnæus. Systema Naturæ, 1767.

Branta. Oken. Lehrbuch der Naturgeschichte, Th. 2, p. 362, 1815.

Malacotta et Senoclita. Schumacher. Essai d'un Nouveau Syst. des Habitations des Vers., 1817.

Otion et Cineras. Leach. Journal de Phys., vol. lxxxv, p. 67, July, 1817.

Gymnolepas. De Blainville. Dict. des Sci. Nat., Art. Mollusca, 1824.

Pamina. J. E. Gray. Annals of Philosophy, vol. x, (Second Series,) August, 1825.[35]

[34] The general title to the volume, containing four Quarterly parts, is dated 1818; but as in the 'Journal de Physique,' for July, 1817, the editor refers to Conchoderma, the Quarterly Part containing this genus must have appeared before 1818: Lamarck gives the year 1814 as the date of the paper in question, and I have accordingly followed him. From a similar reference by the editor, it appears that Schumacher's volume appeared before the number of the 'Journal de Physique' containing Leach's Paper.

[35] Under these nine generic names, the two common species of Conchoderma have received thirty-three different specific denominations, caused partly by changes of nomenclature, and partly from varieties having ranked as species.

Valvæ 2 ad 5, minutæ, inter se remotæ: scuta bi-aut tri-lobata, umbonibus in medio marginis occludentis positis: carina arcuata, terminis utrinque pæne similibus.

Valves 2 to 5, minute, remote from each other: scuta with two or three lobes, with their umbones in the middle of the occludent margin: carina arched, upper and lower ends nearly alike.

Filaments seated beneath the basal articulations of the first pair of cirri, and on the pedicels of four or five anterior pairs; mandibles, with five teeth, finely pectinated; maxillæ step-formed; caudal appendages, none.

Distribution.—Mundane, throughout the equatorial, temperate, and cold seas; attached to floating objects, living or inorganic.

The Capitulum is formed of smooth membrane, including five small valves, of which the terga and carina are often quite rudimentary or absent. Valves minute, thin, generally more or less linear, placed far distant from each other; sometimes imperfectly calcified and covered by chitine membrane, or imbedded in it. The umbones of the valves (together with the primordial valves) are nearly central, so that they are added to at their upper and lower ends; hence their manner of growth is considerably different from that of the valves in Lepas. The adductor muscle is attached to a slight concavity on the under side of each scutum, at the point whence the lobes diverge.

The Terga are placed almost transversely to the scuta; at their lower ends, there is either a very slight prominence in the capitulum, or there is a large tubular, folded appendage, opening into the sack, and apparently serving for respiratory purposes.

Peduncle, smooth, moderately long; attachment effected by the cement-stuff being poured out exclusively, as it appears, from the larval antennæ. These antennæ in C. aurita and C. virgata, resemble, in the form of the disc and in the long feathered spines on the ultimate segment, those in Lepas.

The Filamentary Appendages are highly developed; there are six or seven on each side; two are attached beneath the basal articulation of the first cirrus (as is usual in Lepas), and near them there are one or two small pap-formed projections of apparently similar nature; the rest of the filaments are attached to the posterior edges low down, on the lower segments of the pedicels of the cirri. I believe, in all cases, these appendages are occupied by testes.

Prosoma, moderately developed.

Mouth, situated not far from the adductor muscle; labrum considerably bullate, with the crest hairy and pectinated with inwardly pointing, approximate, flattened teeth: inner fold of the supra-œsophageal cavity slightly thickened and yellowish, villose on the sides.

Palpi of the usual shape, not meeting, moderately broad.

Mandibles, with five teeth, graduated in size, nearly equidistant, finely pectinated either on one or both sides towards their bases; inferior angle narrow, either produced into a fine tooth, or almost rudimentary.

Maxillæ, about 3/4ths of the size of the mandibles, step-formed, with five steps generally distinct; at the upper angle there are two large unequal spines, of which the lower one is the largest, with a third long thin one on the first step; lower spines doubly serrated. Apodeme directed inwards and backwards.

Outer Maxillæ (Pl. X, fig. 16) simply arched; the membrane of the supra-œsophageal cavity under these maxillæ is highly bullate and villose. Olfactory orifices not prominent.

Cirri.—First pair not seated far distant from the second pair. The three posterior pair have the anterior faces of their segments considerably protuberant, supporting four or five pairs of long bristles; between which, there is a row of minute, fine, upwardly pointing bristles: on the lateral upper margins of each segment, there are a few very minute spines; dorsal tuft short, with thick and thin spines intermingled. In the first cirrus (of which the rami are nearly equal in length), and in the anterior ramus of the second cirrus, the faces of the segments are highly protuberant, and clothed with thick transverse rows of finely and doubly serrated spines: the anterior ramus of the second cirrus is considerably thicker than the posterior ramus, which latter, together with both rami of the third cirrus, differ from the three posterior cirri only in the intermediate and in the lateral marginal spines being slightly more developed.

Caudal Appendages, absent.

Alimentary Canal.—The upper part of the stomach has four large cæca, of which the posterior one is the largest; the whole surface, also, is covered with minute pits, arranged in transverse rows.

Generative System, developed to an extraordinary degree. The testes run into all the filamentary appendages, as well as more or less, into the pedicels of the cirri: the two vesiculæ seminales unite within the penis, either just beyond its basal constriction, or up one third of its length. Penis short, hairy. The ovarian tubes not only fill the peduncle, but extend in a thin sheet between the two folds of corium all round the sack, close up to the terga. The two ovigerous fræna are present in the usual position; the ovigerous lamellæ either form several layers, in pairs, one under the other, or are united in a single large cup-formed sheet enclosing the whole animal.

Colours.—The prevailing tint is a dark purplish-brown, which forms, or tends to form, broad longitudinal bands on the peduncle and capitulum.

General Remarks.—This genus is intimately related, as has been remarked by Professor Macgillivray,[36] to Lepas: if we look to the body of the animal, which from being less exposed to external influences must, in the Cirripedia, offer the most trustworthy characters, we find that in Conchoderma there are additional filamentary appendages attached to the cirri, that there are no caudal appendages, that the teeth of the mandibles are finely pectinated, and that the ovarian tubes run higher up round the sack; in every other respect, there is the closest similarity, even to the arrangement of the bristles on the cirri. In the capitulum, the difference consists chiefly, though not exclusively, in the less development of the valves, and their consequent wide separation: the scuta, however, in Conchoderma, are added to beneath their umbones, or original centres of growth, which is never the case, or only to a very slight degree, in Lepas. Conchoderma has no very close affinity to any other genus. As the majority of authors have ranked the two common species under two distinct genera (Otion and Cineras), I may observe, that there is no good ground for this separation; in the above few specified points in which Conchoderma differs from the genus most closely allied to it, the two species essentially agree together. If we take the nearest varieties of C. virgata and C. aurita, there is but a very slight difference even in the form of their valves, and these hold the same relative positions to each other; the carina, however, is always less developed in C. aurita; even the colouring in both tends to follow the same arrangement. The only obvious distinction between the two species, are the ear-like appendages of C. aurita, which, however, are not developed in its early age, are subject to considerable variation, are of no high functional signification, and are indicated in C. virgata by two prominences on the same exact spots. On these grounds I conclude, that the generic separation of the two species is quite inadmissible.

[36] Remarks on the Cirripedia, &c.; 'Edin. New Phil. Journal,' vol. xxxix, p. 171.

1. Conchoderma aurita. Pl. III, fig. 4.

Lepas aurita. Linn.[37] Systema Naturæ, 1767.

Otion Cuvieranus (!) Blainvillianus (!) Bellianus (!) Dumerillianus (!) Rissoanus. Leach. Encyclop. Brit., vol. iii, Supp., 1824, and Zoological Journal, vol. ii, p. 208, July 1825.

Otion depressa et SACCUTIFERA. Coates. Journal Acad. Nat. Sci. of Philadelphia, vol. vi, p. 132, 1829.

Otion auritus. Macgillivray. Edinburgh New Phil. Journal, vol. xxxviii, 1845.

Lepas leporina. Poli. Test. utriusq. Sicil., pl. vi, fig. 21, 1795.

Lepas Cornuta. Montagu. Linn. Trans., vol. xi, p. 179, 1815.

Conchoderma auritum et LEPORINUM. Olfers. Magaz. der Gesell. Freunde zu Berlin, 3d Quartel., p. 177, 1814.

Branta aurita. Oken. Lehrbuch der Naturgesch., Th. 11, p. 362, 1815.

Malacotta bivalvis. Schumacher. Essai d'un Nouveau Syst., &c., 1817.

Gymnolepas Cuvierii. De Blainville. Dict. des Sc. Nat., Art. Mollusc., Plate, fig. 1, 1824.

[37] Many authors (Poli, Montagu, &c.,) have doubted from the strangely mistaken description, viz., "ore octovalvi dentato," whether this species could be the Lepas aurita of Linnæus. But in the Linnean Society, there is a proof plate from Ellis's "Account of several rare Species of Barnacles," in 'Phil. Trans.,' 1758, with an excellent figure of the C. aurita, and on the margin in Linnæus's handwriting is the name Lepas aurita.

C. capitulo duobus tubularibus quasi-auribus instructo, pone terga rudimentalia (sæpe nulla) positis: scutis bilobatis: carinâ nullâ, aut omnino rudimentali: pedunculo longo, a capitulo distincte separato.

Capitulum with two tubular ear-like appendages, seated behind the rudimentary and often absent terga; scuta bilobed; carina absent, or quite rudimentary; peduncle long, distinctly separated from the capitulum.

Filaments attached to the pedicels of the second cirrus; two upper spines of the maxillæ pectinated.

Hab.—Mundane; extremely common. On ships' bottoms from all parts of the world. Arctic Sea. Greenland. Pacific Ocean. Often attached to Coronulæ on Whales. On slow-moving fish, according to Dr. A. Gould. Often associated with C. virgata, and Lepas anatifera, L. Hillii, and L. anserifera.

General Appearance.—The capitulum (seen from above in Pl. III, fig. 4 a) is slightly compressed, almost globular, composed of thick membrane, with two large, ear-like, flexible, tubular, folded appendages, at the upper end, opening into the sack. These appendages are seated behind the rudimentary terga when such are present, or behind the spots which they would have held if not aborted. In a young condition they are tubular, but not folded; and often, according to Prof. Macgillivray, either one or both are at first imperforate. They are formed externally of the outer membrane of the capitulum (rendered thin where folded), and internally of a prolongation of the inner tunic of the sack; between the two, there is, as around the whole sack, a double layer of corium. A section across both appendages, near their bases, is given in Pl. III, fig. 4 b, showing how they are folded,—the chief fold being directed from below upwards, with a smaller fold, not always present, from between the two, outwards. The folds sometimes do not exactly correspond on opposite sides of the same individual; they are almost confined to the lower part, the orifice itself being often simply tubular. These appendages are sometimes very nearly as long as the whole capitulum: a section near their bases is sub-triangular. I shall presently make some remarks on their functions and manner of formation.

The Scuta, as well as the other valves, are imperfectly calcified: shape, variable. They usually consist of two lobes or plates, placed at above a right angle to each other, and rarely (fig. 4 c) almost in a straight line; the lower lobe is more pointed and narrower than the upper; the two correspond to the lower and middle lobes in the scuta of C. virgata, the upper one being here absent.

The Terga are developed in an extremely variable degree; they are often entirely cast off and absent. In very young specimens, they are of the same length with the carina, but after the carina has ceased to grow, the terga always increase a little, and sometimes to such a degree as to be even thirty or forty times as long as carina. When most developed (fig. 4 a) they are not above one third as long as the scuta, to which they lie at nearly right angles; they consist of imperfectly calcified plates, square at both ends, slightly broader and thinner at the end towards the carina, where they are a little curled inwards, than at the opposite end; they are not quite flat in any one plane; internally they are slightly concave; finally, I may add, they nearly resemble in miniature the terga of C. virgata. In full grown specimens, the terga almost invariably drop out and are lost; but even in this case, a long brownish cleft in the membrane of the capitulum, marks their former position. The orifice of the capitulum is usually notched between the terga, or between the clefts left by them; on each side of the notch there is a slight prominence. In some few cases, however, there is no trace of this notch. Behind the terga or the clefts, the great ear-like appendages, as we have seen, are situated.

Carina, rudimentary (fig. 4.) and often absent; it is pointed-elliptical, and is rarely above the 1/40th of an inch long. After arriving at this full size, calcareous matter is added to the under surface over a less and less area, so that it becomes internally pointed, and finally, in place of calcareous matter, continuous sheets of chitine are spread out beneath it; hence, during the disintegration of the outer surface, the carina comes to project more and more, and at last drops out; subsequently, even the little hole in which it was imbedded, disintegrates and disappears.

Peduncle, cylindrical, distinctly separated from the capitulum, and generally twice or thrice as long as it: the thickness of the outer membrane generally great, but variable: surface of attachment variable, either pointed, or widely expanded, or formed into divergent projections.

Filamentary Appendages, seven on each side, highly developed, long and tapering; there are two beneath the basal articulation of the first cirrus, and one on the posterior margin of the pedicel of each cirrus, excepting the sixth pair; the filaments on the pedicels are nearly twice as long as the cirri themselves.

Mouth,—mandibles, with the five teeth nearly equidistant, and towards their bases finely pectinated on both sides; inferior angle rudimentary, often represented by a single minute spine: in one specimen, there were only four teeth on one side. Maxillæ, with five steps, not very distinct from each other, with the first step much curved. The larger of the two upper great unequal spines is pectinated, like the teeth of the mandibles; there is a third long finer spine beneath the upper large pair.

Cirri rather short, broad, with the anterior faces of the segments protuberant, especially those of the first cirrus and of the anterior ramus of the second pair: spines on the anterior cirri doubly serrated. Posterior cirri, with the intermediate spines between the pairs, long; dorsal tufts, minute. On the lower segment of the pedicels of the four posterior cirri, there are two separate tufts of bristles.

Colours extremely variable; sometimes five longitudinal bands of dark purple can be distinctly seen (as in C. virgata) on the peduncle, these bands becoming more or less confluent on the capitulum; at other times, the capitulum is more or less spotted, or often nearly uniformly purple: the sack, cirri and trophi are, also, purple.

Size.—The largest specimen which I have seen was, including the peduncle and ears, five inches in length, the capitulum itself being rather above one inch in length, and 7/10ths of an inch in breadth.

General Remarks.—I have come to the same conclusion with Prof. Macgillivray, concerning the variability of this form, and I believe there is only one true species. With respect to Dr. Coates's species, viz., Otion depressa and O. saccutifera, though I have not seen specimens, I can hardly doubt, from the insufficient characters given, that they are mere varieties.

With respect to the ear-like appendages, we shall presently see in C. virgata, that at corresponding points on the capitulum (Tab. III, fig. 2 b), there are two slight, closed prominences. According to Professor Macgillivray, in C. aurita, every gradation can be followed by which the appendages, at first closed, become tubular and open. The opening would ensue, if the corium became absorbed at the bottom of the appendages whilst still imperforate, for then the inner tunic would be cast off at the next moult and would not be re-formed, whilst the outer membrane would gradually disintegrate together with the other external parts of the capitulum, and not being re-formed at this point, an aperture would at last be left. These appendages have no relation to the generative system: the ovarian tubes, which surround the sack do not extend into them; nor do the ovigerous lamellæ. I believe, that their function is respiratory: the corium lining them is traversed by river-like circulatory channels, and their much-folded, tubular and open structure must freely expose a large surface to the circumambient water. Why this species should require larger respiratory organs than any other, I know not. In this species, moreover, the filamentary appendages are developed to a greater extent than in any other cirripede; in most genera, the surface of the body and of the sack suffices for respiration.

2. Conchoderma virgata. Pl. III, fig. 2. Pl. IX, fig. 4.

Lepas Virgata. Spengler. Skrifter Naturhist. Selbskabet., B. i, 1790, Tab. vi, fig. 9.

—— coriacea. Poli. Test. utriusque Sicil., Pl. vi, fig. 20, 1795.

—— membranacea. Montagu. Test. Brit. Supp., p. 164, 1808, et Linn. Trans., vol. xi, Tab. xii, fig. 2.

Conchoderma Virgatum. Olfers. Magaz. Gesells. Naturfor. Freunde, Berlin, 1814, p. 177, (3d Quartel).[38]

Branta Virgata. Oken. Lehrbuch der Gesell., Th. ii, p. 362, 1815.

Senoclita Fasciata. Schumacher. Essai d'un Nouveau Syst., 1817.

Cineras vittata. Leach. Encyclop. Brit. Supp., Tom. iii, Plate. 1824.

——— cranchii (!) chelonophilus (!) Olfersii (!). Leach. Tuckey's Congo Expedition, p. 412, 1818.

——— megalepis (!) Montagui (!) Rissoanus. _Leach._ Zool. Journal, vol. ii, p. 208, 1825.

——— membranacea. Macgillivray. Edin. New Phil. Journal, vol. xxxix, p. 171, 1845.

——— bicolor. Risso. Hist. Nat. des Productions, &c., 1826, Tom. iv, p. 383.

——— vittatus. Brown. Illust. of Conch., 1844, Pl. li, figs. 16-18.

Gymnolepas Cranchii. De Blainville. Dict. des Sci. Nat. Hist., 1824.

Pamina trilineata (!) (Var. Monstr.). J. E. Gray. Annals of Phil., vol. x, 1825.

[38] See page 136 respecting this date.

C. Scutis trilobatis: tergis intùs concavis, apicibus introrsùm leviter curvatis: carinâ modicâ, leviter curvatâ: pedunculo in capitulum coalescente.

Scuta three-lobed: terga concave internally, with their apices slightly curved inwards: carina moderately developed, slightly curved: peduncle blending into the capitulum.

No filament attached to the pedicel of the second cirrus.

Var. chelonophilus (Pl. III, fig. 2 c). Terga, minute, nearly straight, solid, acuminated at both ends, placed far distant from the other valves: carina, either minute and acuminated at both ends, or moderately developed and slightly arched and blunt at both ends: lateral lobes of the scuta broad: valves imperfectly calcified.

Hab.—Mundane: extremely common on ships' bottoms from all parts of the world. Falkland Islands. Galapagos Islands, Pacific Ocean. Attached to sea-weed, turtle and other objects. Often associated with Conchoderma aurita, Lepas anatifera, L. Hillii, and L. anserifera.

General Appearance. Capitulum, flattened, gradually blending into the peduncle; summit square, rarely obtusely pointed. Membrane, thin. Valves, thin, small, sometimes imperfectly calcified, very variable in shape and in proportional length, and therefore, situated at variable distances from each other, but always remote and imbedded in membrane.

Scuta, trilobed, consisting of an upper and lower lobe (the latter generally the broadest), united into a straight flat disc, with a third lobe standing out from the middle of the exterior margin, generally at an angle of from 50° to 70° (rarely at right angles) to the upper part, and generally (but not always) bending a little inwards. The shape of the lateral lobe varies from rounded oblong to an equilateral triangle; as it approaches this latter form, it becomes much wider than the upper or lower lobes. In one specimen, and only on one side, the scutum (fig. 2 d) presented five points or projections. In some specimens, the scuta are very imperfectly calcified, and consist of several quite separate beads of calcareous matter of irregular shape, held together by tough brown membrane.

Terga, extremely variable in shape, placed at nearly right angles to the scuta: beyond their carinal ends (fig. 2 b), the capitulum presents two small prominences, which are important as indicating the position of the homologous, ear-like appendages in C. aurita.[39] The upper ends of the terga are imbedded in membrane, and project freely like little horns for about one third of their length: this free portion exactly answers to the projecting portion, bounded by the two occludent margins, in the terga of Lepas. The freely projecting portion is generally curled inwards, and the carinal portion more or less outwards,—the form of the letter S being thus approached; but the curvatures are not exactly in the same plane. The whole valve is generally of nearly equal width throughout, the carinal part being a very little (but in some specimens considerably) wider; internally, it is deeply concave; both points generally are blunt and rounded. In some rare varieties (Cineras chelonophilus of Leach, fig. 2 c), the terga are much smaller and flat, with both points sharp, the whole upper portion being much and abruptly attenuated, and internally, without a trace of a concavity. Generally, the terga are about two thirds of the length of the scuta, rarely only half their length; generally, they are separated from the apices of the scuta by about their own length, rarely by twice their own length. Generally, the terga are shorter than the carina, but sometimes a very little longer than it: generally they are distant by one third or one fourth of their own length from the apex of the carina, rarely by their entire length.

[39] These have also been observed by Dr. Coates; see 'Journal of Acad. Nat. Sci. Philadelphia,' vol. vi, p. 134, 1829.

Carina (fig. 2 a), lying nearly parallel to the scuta, concave within, very slightly bowed, of nearly the same width throughout, but with the lower third beneath the umbo, generally a trace wider than the upper part. Length, variable, generally rather longer (sometimes by even one third of its own length) than the scuta, but sometimes equalling only three fourths of the length of the scuta; generally longer than the terga. Upper and lower points rounded; in rare varieties, both ends are sharply acuminated. The carina and terga are generally most acuminated where they are smallest and least perfectly calcified; and consequently, in this same state, the valves stand furthest apart.

Peduncle, flattened, gradually widening as it joins the capitulum, to which it is generally about equal in length, or a little longer.

Filamentary Appendages.—Six on each side (Pl. IX, fig. 4), of which one (h) is seated on the posterior margin of a swelling, beneath the basal articulation of the first cirrus, and this is the longest; the second (g) is short and thick, and is seated a little lower on the side of the prosoma, (near to this, there are also two little pap-like eminences;) the third (i) is seated on the posterior margin of the pedicel of the first cirrus, above the basal articulation; the fourth, fifth, and sixth (j, k, l) in similar positions on the pedicels of the third, fourth, and fifth cirri. These three latter filaments are shorter and smaller than the first three. At the base of the second cirrus, which has no proper filament, there is a swelling as if one had been united to it.

Mouth.—Mandibles, with the basal edges of the five teeth pectinated by minute, short, strong spines on one side; inferior angle extremely short. In one specimen, there was a minute pectinated tooth between the first and second; in another, the second tooth was bifid on its summit; in another, the fourth was rudimentary.

Maxillæ, with five steps: sometimes each step commences with a spine rather larger than the others; at the upper angle, there are two large unequal spines (neither pectinated,) with a third longer and thinner, seated a little below. Outer maxillæ (Pl. X, fig. 16), simple.

Cirri, with twice as many segments in the sixth cirrus as in first; spines on the first and second cirri doubly serrated.

Colours (when alive).—Capitulum and peduncle grey, with a tinge of blue, with six black bands, tinged with purplish brown. The two bands near the carina become confluent on the peduncle, and sometimes disappear; the carina is edged, and the interspace between the two scuta, coloured with the same dark tint. The whole body and the pedicels of the cirri are dark lead-colour, with the segments of the cirri almost black: in some specimens, the colour seems laterally abraded from the cirri. Ova white, becoming in spirits pinkish, and then yellow. The dark bands on the capitulum and peduncle become in spirits purple; but are sometimes discharged; the general grey tint disappears. Professor Macgillivray states that many individuals are light-brown or yellowish-grey, with irregular brown streaks, or crowded dots: he states that in very young specimens the colours are paler, and the valves spicular.

Size.—The largest specimen which I have seen, had a capitulum rather above one inch long and three fourths of an inch wide: growth very rapid.

Monstrous Variety.—In the British Museum, there is a dried and somewhat injured specimen of a monstrous variety, the Pamina trilineata of J. E. Gray: it differs from the common form only in having a tubular projection, just behind the notch separating the upper points of the terga; this tube springs from over the terga, and is, therefore, in a different position from the ear-like appendages in Conchoderma aurita. It does not open into the sack: the membrane composing it appears to have been double in the upper part, and to have been lined with corium: in short, this tube seems to have been an excrescence or tumour, of a cup or tubular form.

General Remarks.—It will have been seen how much subject to variation the valves of this species are. When I first examined the Cineras chelonophilus of Leach, from 36° N. lat., Atlantic Ocean, and found in many specimens, both old and young, that the terga were very small, flat, acuminated at both ends, with a projecting shoulder on the carinal margin, and situated at about their own length from the apex of the carina, and at twice their own length from the scuta; and when I found the carina acuminated at both ends, and the scuta very imperfectly calcified, with the lateral lobe broad, flat, and standing out at right angles; and lastly, when I found the whole capitulum bluntly pointed, instead of being square on the summit, I had not the least doubt, that it was a quite distinct species. Afterwards, I found in the Cineras Olfersii of Leach, from the South Atlantic, the same form of terga; but within slightly more concave or furrowed, and not nearly so small, and therefore not placed at above half so great a distance from the other valves; and here, the carina had its usual outline, as had nearly the scutum on one side, whereas, on the other side, it presented a new and peculiar form, having five ridges or points, and was imperfectly calcified; seeing this, it was impossible to place much weight in the precise form or size (and therefore, relative separation,) of the calcified valves; and on close examination, I found every part of the mouth and cirri identical in Leach's Cineras chelonophilus and C. Olfersii, and in the common form. Therefore, I conclude, that C. chelonophilus, and still more C. Olfersii, are only varieties; the terga presenting the greatest, yet variable, amount of difference, namely, in their acumination and flatness. We know, also, that in the species of the closely allied genus of Lepas, the terga are very variable in shape, and this is the case, even in a still more marked degree, in Conchoderma aurita. Professor Macgillivray, I may add, has come to a similar conclusion regarding the extreme variability of the valves of this species.

As the varieties here mentioned are very remarkable, and may perhaps turn out to be true species, I think they are worth describing in some detail: I will only further add, that we must either make several new species, or consider, as I have done, several forms as mere varieties.

C. virgata, var. chelonophilus of Leach. Pl. III, fig. 2 c.

Atlantic Ocean, 35° 15´ N., 16° 32´ W. On the Testudo caretta.

Capitulum not above half an inch long, composed of very thin membrane, with six bands (as stated by Leach) of faint colour; summit bluntly pointed; valves very small, far distant from each other; the scuta are imperfectly calcified, the central part of the umbo consisting of thick, brown chitine, with imbedded shelly beads; terga and carina perfectly calcified.

Scuta trilobed, flat, within slightly concave, upper lobe rather more acuminated than the lower; lateral lobe triangular in outline, twice as wide as either the upper or lower lobes; lying in the same plane with them and standing out at almost exactly right angle.

Terga, flat; placed obliquely to the scuta, and barely half as long; separated from them by nearly twice their own length; upper and lower points acuminated; the umbo on the carinal margin forms a projecting shoulder; the scutal margin is straight, they are separated by nearly their own length from the apex of the carina.

Carina narrow, very slightly arched, within slightly concave, both points acuminated; lower third rather wider than the upper part; in length equalling three fourths of the scuta, and longer by one third than the terga; about as wide as the latter.

Filaments, Cirri, and Mouth exactly as before.

In some specimens sent to me by the Rev. R. T. Lowe from off the Testudo caretta, taken near Madeira, the scuta have their lateral lobes broad and nearly rectangular: the carina extends nearly to between the terga: the terga are nearly straight, somewhat pointed at both ends, distant from the scuta, almost solid within, with their upper points bowed outwards: the whole capitulum is bluntly pointed, as in the var. chenophilus, to which form this makes a rather near approach.

C. virgata, var. Olfersii.

Cineras Olfersii. Leach. Tuckey's Congo Expedition.

Hab. South Atlantic Ocean.

Scuta, unlike on the opposite sides of the same individual, on one side with a single lateral lobe as usual, but this very narrow, on the other (fig. 2 d), with five lobes or projections.

Terga slightly concave within, separated by a little more than their own length from the tips of the scuta, and by one third of their own length from the tip of the carina.

Carina longer than the scuta by about one fifth or one sixth of its own length, blunt at both ends, considerably bowed.

Again, I possess a group of remarkably fine specimens given me by Mr. L. Reeve, from the southern ocean, (as I infer from a young Lepas australis adhering to them,) in which all the individuals, young and old, are characterised as follows:—Scuta, with the lateral lobe generally broad, but to a very varying extent, with the upper and lower lobes extremely sharp. Terga separated from the scuta, by one and a fourth of their own length, and by their own length from the carina; somewhat acuminated at both ends, nearly straight, with a very slight shoulder near the umbo. Carina equalling the terga in length, and about three fourths of the length of the scuta; neither the upper nor lower point much acuminated. All the valves most imperfectly calcified: in one specimen, the scutum on one side was simply horny, without a particle of calcareous matter. The summit of the capitulum nearly intermediate in outline between the common square, and bluntly-pointed form of var. chelonophilus. I compared the cirri and trophi with those of a common variety, and could detect not the smallest difference. This variety differs from var. Olfersii, in the less development of its carina, and from chelonophilus, in the greater development of its carina, and especially of its terga. It would appear as if the great variability of the valves was connected with the absence of calcareous matter.

3. Conchoderma Hunteri. Pl. III, fig. 3.

Cineras Hunteri. R. Owen. Cat. Mus. Coll. of Surgeons, (1830), Invert. Part I., p. 71.

C. valvis angustis: scutis trilobatis, prominentiâ laterali non latiore quam inferior: tergorum parte superiore pæne rectangulè secundùm aperturæ marginem flexâ: carinâ valde arcuatâ: pedunculo brevi, in capitulum coalescente.

Valves, narrow: scuta, trilobed, with the lateral lobe not wider than the lower one: terga, with the upper part bent almost rectangularly along the margin of the orifice: carina considerably arched: peduncle short, blending into the capitulum.

No filament attached to the pedicel of the second cirrus.

Var.—Carina absent; scuta, with the upper lobe absent; terga, with the rectangular projection little developed.

Attached to the skin of a snake, probably the Hydeus or Pelamis bicolor, and therefore from the tropical Indian or Pacific Oceans. Mus. Coll. of Surgeons.[40]

[40] I owe to the kindness of Professor Owen, an examination of these specimens, and information regarding them.

Capitulum, with the membrane very thin; summit obtusely pointed. Valves linear and thin.

Scuta, elongated, flat, with the upper projecting lobe rather more acuminated than the lower, and equalling it in length; lateral lobe not wider than the lower, and about as long as it, forming an angle of about 55° with the upper one.

Terga, of somewhat variable length, generally about half as long as the carina, narrow, and of nearly equal width throughout; lower point sharp; externally convex; internally solid, with a trace of a central depressed line; the upper fourth part generally a little bowed out of the plane of the lower part, and abruptly bent at rather above a right angle along the occludent margin of the orifice. These valves are situated at about half their own length from the upper points of the scuta.

Carina considerably arched, extending to the lower points of the terga, or running up between them for even half their length; equally narrow throughout; scarcely broader than the terga; both points rounded; internally concave; the lower point does not extend as far down as that of the lower lobe of the scuta.

Peduncle, narrow, shorter than the capitulum, which, in the largest specimen was 4/10ths of an inch long. Longitudinal purple bands appear to have originally existed on the peduncle.

Filamentary Appendages, trophi and cirri all similar to the same parts in C. virgata; but perhaps the anterior faces of the segments in the posterior cirri are rather less protuberant; perhaps also the first cirrus is rather shorter in proportion to the sixth cirrus.

Variety (monstrous).—Amongst the specimens, I found one very young one, in which the scuta had not upper lobes, so that in outline they exactly resembled the scuta in the quite distinct C. aurita: there was not even a rudiment of a carina: the tergum, on one side, was externally bordered by a projecting, semicircular, calcified disc; and the upper points of both terga showed only traces of the rectangular projection, which is the chief characteristic of C. Hunteri. From these traces alone, and from the specimen being mingled with the others, do I here include this variety.

General Remarks.—I have very great doubts whether I have acted rightly in considering this as a species; but as there were many specimens, old and young, all differing remarkably from the common species, this form anyhow deserves description. The points by which it can be distinguished from C. virgata, are—the almost rectangular manner in which the upper portion of the tergum is bent outwards and along the orifice of the sack—the narrowness of all the valves, and especially of the lateral lobes of the scuta,—and lastly, the greater curvature of the carina, which in some specimens runs up far between the terga; had this last character been constant, it would have been an important one, but such is far from being the case. Great as are these differences in the valves, and though common to many specimens, they are not sufficient to convince me that it is a true species, and I should not be at all surprised at varieties, intermediate between it and the common form, being hereafter found;—had a name not been already attached to it, I should not have given one. In the monstrous variety described, we see to what an extent the valves may vary. The C. Hunteri approaches nearest to the var. of C. virgata, called by Leach Cineras chelonophilus, for in both, the top of the capitulum is bluntly pointed and the terga are solid within; in the Var. chelonophilus, the terga and carina are minute, whereas here, though very narrow, they are much elongated. Certainly C. chelonophilus has almost as strong a claim to rank as a species as C. Hunteri; but, in the former, by the aid of other varieties, the differences were almost reduced to the peculiarities in the terga—the valves, the most subject to variation. In C. Hunteri we have other differences, and the form of the terga is even still more peculiar. I have, therefore, provisionally attached to it the specific name by which it is designated in the Museum of the College of Surgeons. From having been long kept in spirits, all aid from colour is lost.

Genus—Alepas. Pl. III.

Alepas. Sander Rang. Manuel des Mollusques, 1829.

Anatifa. Quoy et Gaimard. Voyage de l'Astrolabe, 1834.

Triton. Lesson. Voyage de la Coquille, 1830.

Cineras. Lesson. Secundum Sander Rang.

Capitulum aut sine valvis, aut scutis corneis, pæne abditis.

Capitulum without valves,[41] or with horny, almost hidden, scuta.

[41] Any one not attending to the characters derived from the softer parts of the Balanidæ and Lepadidæ, might easily confound with Alepas the genus Siphonicella (genus nov.), which, undoubtedly, though having the external appearance of a pedunculated cirripede, belongs to the Balaninæ, and is closely related to Coronula.

Filaments seated beneath the basal articulations of the first pair of cirri; mandibles, with two or three teeth; maxillæ notched, with the lower part irregular, projecting; caudal appendages multi-articulate.

Attached to various living objects, fixed or floating.

Capitulum either entirely destitute of valves, or with transparent horny scuta, not containing any calcareous matter, and almost hidden in membrane. These scuta are formed of a lower and a lateral lobe, placed at above right angles to each other; they are added to by successive layers, and closely resemble in shape the scuta of the Conchoderma aurita. The orifice in A. tubulosa projects so much as to be almost tubular. In A. parasita and A. minuta it does not project, and is either moderately large, or very small in proportion to the length of the capitulum; from contraction it is much wrinkled. The membrane forming the capitulum is smooth and very transparent; it contains very few tubuli, except under certain irregular projections in A. cornuta.

The Peduncle is rather short and narrow; it blends into the capitulum, and is not, in some of the species, separated from it by any distinct line; the surface of attachment is rather wide. Within the peduncle we have the three usual layers of striæ-less muscles; namely, the innermost and longitudinal, which run lower down than the others; the middle and transverse; and, lastly, the exterior, oblique muscles, which cross each other (becoming transparent) on the rostral central line. These several muscles run up from the peduncle and surround the capitulum; from the transparency of the membranes they can be seen from the outside: they are particularly conspicuous round the orifice, which they probably serve to close. There is, in all cases, the usual adductor scutorum muscle (with transverse striæ), which is attached under the horny scuta, where such exist. The fact of the striæ-less muscles of the peduncle surrounding the whole capitulum, has been observed only in one other genus, namely Anelasma. In consequence of this structure, the capitulum must possess considerable powers of contraction.

The antennæ of the larva in the Alepas cornuta and A. minuta have the sucking disc nearly circular, with the spines unusually plain on the distal as well as proximal margin. Basal segment broad, much constricted where united to the disc. The ultimate segment has on the middle of the outer margin, in A. cornuta, two minute spines, which I have not observed in any other cirripede: on the summit there are the usual spines.

Size.—Three of the species are small.

Filamentary Appendages.—These are rather small; there is only one on each side, situated on the posterior margin of a slight swelling, beneath the basal articulation of the first cirrus; and therefore in the position in which the filaments are most constant in Lepas, and where they likewise occur in Conchoderma.

Body.—The prosoma is either pretty well developed or is small, according as the first cirrus is placed near to, or far from the second cirrus.

Mouth.—Labrum moderately bullate, with the lower part more or less produced; crest with blunt, bead-like teeth, and short hairs.

Palpi (Pl. X, fig. 8), acuminated and narrow to an unusual degree.

Mandibles, with two or three teeth, and the inferior angle acuminated; the lateral bristles unusually strong, so as to give the main teeth the appearance of being pectinated.

Maxillæ, widely notched, with three great upper spines; the part beneath the notch projecting, and either straight or irregular.

Outer Maxillæ, with the inner bristles either continuous or divided into two groups: exteriorly there is a smaller or larger prominence, with long bristles. The olfactory orifices are either slightly, or not at all protuberant.

Cirri.—In the three posterior pair, the segments have their bristles arranged in a transverse row, either in the form of a narrow brush, or consisting only of a single pair with two or three minute, intermediate, and lateral marginal spines. The anterior ramus of the second cirrus is thicker, and more thickly clothed with spines than is the posterior ramus: this latter ramus, however, and both rami of the third cirrus, are rather more thickly clothed with spines than are the three posterior pair. The unique case in A. cornuta of the inner rami of the fifth and sixth cirri being rudimentary (Pl. X, fig. 28) will be minutely described under that species.

Caudal Appendages, thin, tapering, multi-articulate, about as long as the pedicels of the sixth cirrus.

Stomach.—The œsophagus runs in a somewhat sinuous course, and enters the top of the stomach obliquely. There are no cæca. The biliary envelope presents a reticulated structure, instead of the usual longitudinal folds.

Generative System.—The penis is hairy, not very long, and ringed or articulated in an unusually plain manner; the space between each ring being about one fourth of the diameter of the penis: the unarticulated basal portion or support is here remarkably long. The vesiculæ seminales are long, tortuous, and enter the prosoma. The ovarian tubes are of wide diameter: in A. cornuta they surround the whole capitulum. The ovigerous fræna are small, constricted at the base, and square on the free margin, which is studded with minute glandular beads, borne on the finest footstalks.

Range.—Southern shores of England, Mediterranean, Atlantic, West Indies, New Zealand, attached to various objects. A. parasita has been always taken on Medusæ.[42]

[42] It appears that Solander (Dillwyn Des. Cat., vol. i, p. 34) observed a species of this genus adhering to a Medusa on the coast of Brazil. Mr. Cocks informs me that an Alepas, apparently A. parasita, has been cast on shore near Falmouth, attached to a Cyanæa; and that two other specimens adhered to the bottom of a vessel arriving at that port from Odessa.

Affinities.—This genus differs from all, except Anelasma, in the manner in which the striæ-less muscles of the peduncle run up and surround the capitulum, and likewise in the reticulated character of the biliary envelope of the stomach. To Conchoderma, especially to C. aurita, there is manifest affinity in the form of the horny scuta: there is also some affinity to this same genus in the presence of filamentary appendages though here little developed, and in the circular form of the disc of the larval antennæ, and, lastly, in the ovarian tubes in A. cornuta surrounding the capitulum. There is quite as close, if not closer affinity to Ibla, in the following peculiarities,—in the curved œsophagus,—in the general character of the cirri and trophi, with the olfactory orifices in one species in some degree prominent,—in the multi-articulated caudal appendages,—and in the plainly-articulated penis, with its elongated unarticulated support, though both these characters are exaggerated in Ibla. Lastly, the scuta in Ibla, though not at all resembling in shape those of A. cornuta, are formed without calcareous matter; and again, in Ibla, the muscles of the peduncle run up to the bases of the valves, and so almost surround the space in which the animal's body is lodged.

The four species of Alepas appear to form two little groups; viz. A. parasita and A. minuta on the one hand, and A. cornuta and A. tubulosa on the other.

1. Alepas minuta. Tab. III, fig. 5.

Alepas minuta. Philippi. Enumeratio Mollusc. Siciliæ, 1836, Tab. xii, fig. 23.

——— ——— A. Costa. Esercitazione Accadem., vol. ii, part I, Naples, 1840, Pl. iii, fig. 5 (secundum Guerin in Revue Zoolog., 1841, p. 250.)

——— ——— Chenu. Illust. Conch., Pl. iii, figs. 8-10.

A. aperturâ non prominente, capituli longitudinis vix tertiam partem æquante: scutis corneis, pæne absconditis: longitudine totâ ad quartam unciæ partem.

Orifice not protuberant, one third of the length of the capitulum: scuta horny, almost hidden. Total length quarter of an inch.

Outer maxillæ, with the spines in front continuous; posterior cirri, with several long spines arranged in a transverse row on each segment; caudal appendages longer than the pedicels of the sixth cirrus.

Sicily; attached to a Cidaris:[43] island of Capri (A. Costa).

[43] I am greatly indebted to Professor J. Müller, of Berlin, for kindly lending me specimens.

Capitulum oval, blending insensibly into the peduncle; moderately flattened; composed of thin structureless membrane, with the exception of two horny, almost quite hidden scuta. Orifice situated near the summit, and in a line, which is oblique to the longitudinal axis of the peduncle; much wrinkled; barely one third of the length of the whole capitulum.

The Scuta, consist of yellowish, transparent, horny, laminated chitine, without any calcareous matter; externally covered by the common integument of the capitulum; these valves are placed very near to each other, close under the orifice, and therefore high up on the capitulum; the membrane between them is smooth and unwrinkled; they are formed of two rather acuminated lobes, joining each other at above a right angle; one lobe (the longer one) stretching nearly transversely across the capitulum, the other running down parallel to its rostral margin: in shape and position they resemble the scuta of Conchoderma aurita; and if another lobe had been developed it would have run along the orifice, and then these valves would have resembled the scuta of Conchoderma virgata. In a specimen with a capitulum 2/10ths of an inch long, the scuta from point to point were 1/20th of an inch in length.

Peduncle, much wrinkled, about one third in diameter of the capitulum, and shorter than it; at the base it is generally expanded into two or three finger-like projections. Length of the largest specimen, about one fourth of an inch. Colour, according to A. Costa in the work above cited, "rufo-flava vittatâ;" but after spirits the whole becomes uniformly yellowish.

Filamentary Appendages, situated beneath the basal articulation of the first cirrus, on the posterior edge of the usual enlargement; acuminated, about two thirds of the length of the shorter ramus of the first cirrus.

Prosoma well developed.

Mouth.—On each side there are two slight prominences; one under the mandibles, the other transverse nearer to the adductor muscle.

Labrum, placed near the adductor muscle, with the upper part not more bullate than the lower part; crest with a row of blunt teeth, and many fine bristles growing chiefly outside the teeth; there are many fine bristles on the inner or supra-œsophageal fold of the labrum.

Palpi not nearly touching each other, pointing towards the adductor: much hollowed out on their inner sides, hence narrow and acuminated, with doubly serrated bristles.

Mandibles, with three teeth and the inferior angle ending in a single sharp spine; whole inferior portion narrow; first tooth as far from the second, as the latter from the inferior angle; owing to the presence of short thick spines projecting from the sides of the jaw, the lower edges of the second and third teeth appear pectinated.

Maxillæ, nearly two thirds of the width of the mandibles; beneath the three larger upper spines there is a considerable notch, and the whole lower part is very slightly upraised; edge irregular, with obscure traces of either two projections, or perhaps of four steps.

Outer Maxillæ, with bristles in front continuous; exteriorly there is a slight prominence near each olfactory orifice, with a tuft of long bristles.

Cirri not much elongated; first pair placed not quite close to the second; five posterior cirri nearly equal in length; pedicels long, with irregularly scattered spines,—those on the pedicel of the first cirrus beautifully and conspicuously feathered. The segments of the three posterior pair are not very short or broad; very slightly protuberant, each with a long transverse, crescentic, narrow brush of bristles, which stand two or three deep in the middle, but on the sides are single: dorsal tufts long, and in the upper segments the spines are thick and claw-like. This structure is common to all the cirri. First cirrus with the rami unequal in length by two segments; from the shortness of the pedicel, this cirrus is much shorter than the second, but its rami are about two thirds of the length of those of the second cirrus. Second cirrus (and in a less degree the third cirrus), with the anterior ramus a shade broader than the posterior ramus, and rather more thickly covered with spines than are the three posterior cirri. Fifteen segments in the sixth cirrus; nine in the longer ramus of the first cirrus.

Caudal Appendages, rather longer than the pedicels of the sixth cirrus, composed of seven cylindrical, tapering segments, each with a circle of very fine bristles on its summit.

The acoustic (?) sacks are situated some way below the basal articulations of the first cirrus.

2. Alepas parasita.

Alepas parasita. Sander Rang. Man. des Mollusq., p. 364, Pl. viii, fig. 5, 1829.[44]

Anatifa univalvis. Quoy et Gaimard. Annales des Sciences, Nat., tom. x, p. 234, 1827, Pl. vii, fig. 8.

——— parasita. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, 1834.

Triton (Alepas) fasciculatus. Lesson. Voyage de la Coquille. Mollusc. Pl. xvi, fig. 6, tom. ii, part I, 1830, p. 442.

[44] M. Sander Rang rejects the specific name "univalvis," as signifying a generic character, and he has been followed in this by MM. Quoy and Gaimard themselves. This, according to the Rules of the British Association, would hardly have been a sufficient reason, but it appears that A. parasita, like A. minuta, has a pair of horny scuta or valves; and, therefore, the name univalvis is too obviously false to be retained. With respect to the generic name Triton, I fully believe that it was applied by Linnæus to the cast-off exuviæ of sessile Cirripedes.

A. aperturâ non prominente, capituli longitudinis 2/3 æquante: scutis corneis: longitudine totâ ad 2 uncias.

Orifice not protuberant, equalling two thirds of the length of the capitulum: scuta horny. Total length two inches.

Animal unknown.

Parasitic on Medusæ, Mediterranean and Atlantic Oceans: south shore of England(?)[45]

I have not seen this species, and have drawn up the above specific character from the Plates and brief descriptions in the Voyages of the Coquille and Astrolabe. M. Lesson thinks that his species differs from that of MM. Quoy and Gaimard; but as the peculiar yellow colour of the capitulum, general shape, short cirri, habits and range, are all common to both, I believe that they are identical. There is, however, one singular difference, namely, that the cirri are coloured bright blue in the Plate in the Voyage of the Astrolabe, and yellowish in that in the Voyage of the Coquille: this possibly may have resulted from the drawing in the latter case having been made from a specimen long kept in spirits.

M. Lesson says that there are seven pair of cirri, from which I infer that this species has a pair of long, articulated, caudal appendages: he asserts that each cirrus has ten segments; the cirri are short and little curled. M. Lesson remarks, that "deux languettes bifurques occupent le bas de l'ouverture ovale:" I can hardly doubt but that these are horny scuta of nearly the same shape as in A. minuta. The whole animal seems to be extremely transparent, and of a "jaune-citron clair." MM. Quoy and Gaimard, however, remark, that different specimens vary from white to yellow. Entire length two inches, of which the capitulum is fourteen French lines. The peduncle is narrow and short.

[45] See Foot-note, p. 159.

3. Alepas cornuta. Pl. III, fig. 6.

A. aperturâ parvâ, leviter prominente: scutis nullis: capitulo plerumque tribus, parvis, compressis eminentiis secundum carinalem marginem instructo.

Orifice small, slightly protuberant; capitulum without horny scuta; generally with three small flattened projections along the carinal margin.

Outer maxillæ with the inner bristles divided into two groups; segments of the posterior cirri extremely numerous, each with one pair of main spines; inner rami of the fifth and sixth cirri rudimentary.

St. Vincent's, West Indies, attached to an Antipathes, collected by the Rev. L. Guilding.

Capitulum globular, slightly flattened, smooth, translucent, entirely destitute of valves; orifice slightly projecting or tubular, parallel to the longitudinal axis of the peduncle, with the edges sinuous; it appears more tubular than it really is, from the convexity of the part of the capitulum immediately beneath the orifice. Three small, flexible, horny, irregular prominences project from the carinal margin; one at the bottom of the capitulum; a second about half-way up it; and a third generally close to the orifice; but their positions vary a little, and the prominences vary still more in shape and size, being either rounded and very small, or much flattened and considerably prominent; they are imperforate; in the membrane under them a few tubuli may be seen, which are not elsewhere visible; their summits are roughened with very minute points and beads of chitine; others, still minuter, are scattered over the whole capitulum.

Peduncle short, narrower than the capitulum, into which it insensibly blends; strongly wrinkled; surface of attachment wide; position with respect to the branches of the coralline, various.

Size and Colour.—The largest specimen, including the peduncle, was half an inch in length, and 3/10ths of an inch across the capitulum; colour, after having been long in spirits, brownish-yellow.

Filamentary Appendages, one on each side, short, tapering and pointed; seated on the posterior margin of a slight swelling beneath the basal articulation of the first cirrus; they are about equal in length to the pedicels of this cirrus.

The Mouth is directed abdominally; labrum much produced downwards, so as to be far separated from the adductor muscle; moderately bullate, forming about one third of the longitudinal axis of the entire mouth; upper part forming a slightly overhanging prominence; crest with a row of blunt, bead-like teeth, and externally to them there are numerous curved short bristles.

Palpi (Pl. X, fig. 8,) unusually narrow, a little hollowed out along their inner margins; pointing towards the adductor muscle; thickly covered with doubly serrated bristles.

Mandibles, with either two or three teeth; inferior angle narrow and tooth-like; both sides covered with strong bristles or spines, projecting beyond the toothed edge.

Maxillæ, with two large upper spines, and a third rather distant from them; beneath these, there is a wide notch or hollow; inferior part square, projecting, bearing six pair of moderately long spines, (of which the central one is the longest,) mingled with finer ones.

Outer Maxillæ, with a semicircular outline; the serrated bristles in front are divided into two groups; externally there is a rounded and very considerable projection covered with long bristles. Olfactory orifices slightly prominent, approximate, seated within and just beneath the rounded projections at the base of the maxillæ.

Body.—Prosoma little developed; thorax small.

Cirri, extremely long, but slightly curled, capable of being protruded so as almost to touch the base of the peduncle or the surface of attachment; segments short, extraordinarily numerous. In the three posterior cirri (excepting the rudimentary rami), each segment supports two long, slightly serrated spines, with two or three minute intermediate ones, and with one or two very short, thick spines on the inner and upper lateral margins: dorsal tufts with only two or three long, fine, unequal spines. All the segments are extremely flat, broad, short, with their anterior faces not protuberant; the greater number of the segments, especially the lower ones, have very obscure articulations, to be seen only with a high power, and these can be capable of little or no movement.

First Cirrus placed far from the second, with the top of its pedicel on a level with the top of the lower segment of the pedicel of the second cirrus; rami short, barely half the length of those of the second cirrus; unequal, the anterior ramus being only two thirds of the length of the posterior one; the shorter ramus contains thirteen inverted-conical segments, with one side rather protuberant; the longer ramus contains twenty-three thinner segments; the segments on both rami are clothed with bristles, arranged in two or three rows, forming narrow transverse brushes.

Second Cirrus, with its pedicel long, and its rami nearly equalling in length those of the sixth pair; the two rami of nearly equal length; the anterior one rather thicker than the posterior one; this posterior ramus has fifty-five segments! The bristles on the second and third cirri are arranged on the same principle as on the three posterior pair; but from an increase in size and number of the little intermediate bristles between the main pairs, and of those on the lateral rims, the segments, especially the basal ones, of the anterior ramus of the second cirrus, are clothed with thin brushes of bristles; these same bristles, on the posterior ramus of the second, and on both rami of the third cirrus, can hardly be said to form brushes, though longer and more numerous than those on the three posterior pair of cirri.

Fifth and Sixth Cirri.—These resemble each other, and have their inner or posterior rami in an almost rudimentary condition. In the sixth cirrus (Pl. X, fig. 28) the outer ramus (a) has actually sixty-three segments, whereas the rudimentary ramus (k) has only eleven, nearly cylindrical segments. These are furnished with extremely minute spines, of which those on the dorsal face are longer than those on the anterior face; the spines on the summit of the terminal segment are the longest; the segments are not half as thick as the normal ones in the outer ramus. The rudimentary ramus is only one seventh part longer than the pedicel which supports both it and the normal ramus. In the fifth cirrus, the rudimentary ramus is rather longer, and has thirteen segments, resembling those in the rudimentary ramus of the sixth. In the fourth cirrus there is no trace of this peculiar structure, the rami being equal in length and strength. The two rudimentary rami on each side are nearly straight, and seem incapable of movement; they project out behind the normal rami, and closely resemble in general appearance, the two caudal appendages; hence this cirripede, at first sight, appears to be six-tailed.

Pedicels of Cirri.—The pedicel of the first pair is very short; that of the second is the longest; those of the posterior cirri decreasing in length. Upper segments short; lower segments in the second, third and fourth cirri, irregularly and rather thickly clothed with bristles, but in the fifth and sixth cirri, there is a regular double row of main spines, with some minute intermediate ones: hence there is a difference, both in the rami and in the pedicels, between the fourth cirrus and the fifth and sixth, and this is a unique case. On the dorsal surface of the pedicel of the second cirrus, there is a tuft of much feathered fine spines.

Caudal Appendages.—Each consists of eight much tapering, very thin segments, furnished with a few short simple spines round their upper margins, and with a longer tuft on the terminal short segment; basal segments twice as thick as the middle ones. In length, these caudal appendages equal the pedicels of the sixth pair of cirri, and are a very little shorter than the rudimentary rami of these same cirri.

General Remarks.—Having examined this species first in the genus, I fully anticipated that the very remarkable character of the inner rami of the fifth and sixth cirri being rudimentary, and serving the same function (if any) with the caudal appendages, would have been generic; but this is not the case, for Alepas cornuta cannot be separated from A. minuta without violating a clear natural affinity.

4. Alepas Tubulosa.

Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, fig. 5, 1834.

A. aperturâ parvâ prominente et tubulosâ: scutis et prominentiis secundùm marginem carinalem, nullis.

Orifice small, tubular, protuberant; capitulum without horny scuta or projections along the carinal margin.

Animal unknown.

New Zealand, Tolaga Bay. Attached to a living Palinurus.

I have given the above brief character from the plate, and imperfect description in the voyage of the Astrolabe. The small and distinctly tubular orifice, and the smooth carinated edge of the globose capitulum, appear sufficiently to distinguish this species from A. cornuta. The colour is stated to have been white with violet tints. Length, two (French) lines.

Anelasma. Gen. Nov. Pl. IV.

Alepas. Lovén. Ofversigt of Kongl. Vetenskaps-Akad. Fördhandlinger: Forsta Argangen. Stockholm, 1844, p. 192, Tab. 3.

Capitulum sine valvis: aperturâ amplâ: pedunculus fimbriatus, sub-globosus, infossus.

Capitulum without valves; aperture large; peduncle fimbriated, sub-globular, imbedded.

Cirri without spines; outer maxillæ and palpi rudimentary, spineless; mandibles minute, with several small teeth irregularly placed; maxillæ minute, with very minute irregularly scattered spines. No caudal appendages.

I owe to the great kindness of Professor Steenstrup, an examination of this very curious cirripede, well described and figured by Lovén, who considered it an Alepas. It lives parasitic, with its peduncle imbedded in the skin of sharks, in the North Sea. According to the principles of classification which I have followed, this cirripede cannot possibly remain in Alepas, and must form a new genus; for some time, indeed, I thought that a new family or sub-family ought to have been instituted for its reception; but when I considered that its highly peculiar characters are all negative, as the non-articular, non-spinose structure of the cirri, and that no new or greatly modified functional organ is present, I concluded that it might properly remain amongst the Lepadidæ. We shall, moreover, hereafter see that the male of Ibla, which, of course, must remain in the same family with the female, is, in some analogous respects, even more abnormal than Anelasma.

1. Anelasma squalicola. Pl. IV, figs. 1-7.

Alepas squalicola. Lovén, ut supra.

North Sea. Parasitic on Squalus.

Capitulum, destitute of valves; oval, much flattened; the double membrane composing it, thin, highly flexible, coloured externally and internally, by the underlying corium, of a blackish purple; aperture, extremely large, extending from the upper end of the capitulum, to close above the peduncle, gaping, and not protecting (in the dead condition) the cirri and mouth.

The Peduncle is about half as long as the capitulum, but, according to Lovén, this part varies in length; it is a little narrower than the capitulum; colourless, from being imbedded in the shark's skin; sub-globular; basal end almost hemispherical. Total length of animal 1.3; diameter of peduncle .4 of an inch.

The external membrane of the capitulum is not nearly so thick as is usual in other Cirripedes, and is, therefore, unusually flexible. The internal membrane, on the other hand, is very much thicker than is usual, being only a little thinner than the outside coat; this circumstance, as well as the similarity in colour on both sides, is evidently due to the remarkable openness of the sack, and consequent exposure of its inside. The inner membrane, when viewed under a high power, is seen to be covered with the minutest spines; the external membrane is structureless, except that there are a few rows of very minute beads of hard chitine, like those which occur on the capitulum of Conchoderma aurita. Lovén, however, states that there are imbedded in the outer membrane, scattered, minute, dendritic, calcareous particles. Of these, I could see no trace. There is a very thin muscular layer between the two coats, all round the capitulum, and this layer becomes rather thicker round the base, near the peduncle. The adductor muscle, occupying its usual place close below the mouth, is thinner than in any other Cirripede of the same size seen by me; nor does it end so abruptly at each extremity, as is usual: where attached to the outer coat, no impression is left. It is a singular fact, that in this Cirripede alone, the fibres of the adductor, and of the muscles of the cirri, and of the trophi of the mouth, are destitute of transverse striæ; but it is not singular, that the muscles surrounding the capitulum should, also, be destitute of striæ, for this is the case with the muscles which, running up from the peduncle, surround the capitulum in Alepas, and partly surround it in Conchoderma. It must not be inferred from the absence of transverse striæ in the muscular fibres of the adductor and of the cirri and trophi, that they are involuntary, but only that they are in an embryonic condition, for I find in the natatory larva, that all the muscles, with the exception of some connected with the eyes, are similarly destitute, and yet perform voluntary movements.[46]

[46] Dr. C. Schmidt in his Contribution to the comparative Anatomy of the Invertebrate animals, &c., (translated in Taylor's Scientific Memoirs, vol. v, p. 1,) says that in young Crustacea, "we find plain primitive fibres, which subsequently acquire the transversely striated aspect."

Although in the dead state, the aperture of the capitulum seems to be always gaping, yet I have little doubt, that the living animal can fold the flexible membrane, like a mantle, round its thorax and cirri, and thus protect, though feebly compared with most Cirripedes, these organs. I suspect that the mouth is always exposed.

Peduncle.—The membrane of the peduncle is thin; the whole surface is sparingly and quite irregularly studded with minute, much-branched filaments (Pl. IV, fig. 3, highly magnified); these are occasionally as much as l/5th of an inch in length; the degree of branching varies much, but is generally highly complex; the ordinary diameter of the branches is about 1/200th of an inch; their tips are rounded, and even a little enlarged, and frequently torn off, as if they had been attached to or buried in the flesh of the shark, in which the whole peduncle is imbedded. These filaments are formed of, and are continuous with the external transparent membrane of the peduncle, and they contain, up to the tips of every sub-branch, a hollow thread of corium, prolonged from the layer internally coating the whole peduncle. In all other Lepadidæ, the peduncle increases in length, chiefly at the summit where joined to the capitulum, and in diameter, throughout nearly its whole length, except close to the base; but, owing to the constant disintegration of the outer surface, the old outside coat does not split in defined lines, like the membrane of the capitulum. In Anelasma, however, owing to the imbedded position of the peduncle, the old outer coats are preserved, the lines in which they have split during continued growth being thus exhibited: those in the uppermost part almost symmetrically surround the peduncle, showing that here, as in other Lepadidæ, has been one regular line of growth; but in the lower part the lines are extremely irregular; and what is almost unique, it appears that the blunt basal end is constantly increasing in length and breadth, and, apparently, at a greater rate than any other part. I judge of this latter fact, from the whole bottom of the peduncle being covered with numerous curved, or nearly circular, lines of natural splitting, the nature of which can be best understood by examining the much-enlarged drawing (Pl. IV, fig. 3) of a small portion (taken by chance) of the membrane of the base, seen from the outside, and bearing some of the simplest branched filaments: other branches, as may be seen, have been cut off. This manner of growth explains the broad, blunt basal termination of the peduncle, so unlike that in other Lepadidæ. New membrane is formed, not continuously as in other cases, under the whole surface of the old membrane, but in irregular patches; thus the portion marked (a) runs under (b), but not under the little circles (c, c), for these are the last-formed portions and underlie the membrane (a) and (b). I do not understand how the splitting of the old membrane is effected; but no doubt it is by the same process by which the membrane of the capitulum in other genera, as in Scalpellum, splits symmetrically between the several valves. In the branched filaments it is particularly difficult to understand their growth, for it is not possible, after examining them, to doubt that they continue to increase, and send off sub-branches, which it would appear probable, penetrate the shark's flesh like roots. I may remark that one, or more commonly two or three branched filaments stand nearly in the centre of each circular line of exuviation or splitting. The branched filaments first commence as mere little pustules, and these appear to be most numerous at the bottom of the peduncle.

The final cause of the downward growth of the bottom of the peduncle, is obviously to allow of the animal burying itself in the shark's body, in the same way as Coronula and Tubicinella become imbedded by the downward growth of their parietes in the skin of Cetacea. The only other genus of Lepadidæ, in which the growth of the peduncle is at all analogous, is Lithotrya, in this genus, however, the animal burrows mechanically into soft rock or shells.

I looked in vain for cement, or for the cement-glands, (but the specimen was in an extremely unfavorable state for finding the latter) or for the prehensile antennæ of the larva. No doubt this Cirripede at first becomes attached in the same way as others, but after early life, I suspect it is retained in its place, by being so deeply imbedded in the shark's body, and perhaps by the root-like branched filaments. The irregular growth and splitting of the membrane at the base of the peduncle, where the prehensile antennæ of the larva must originally have been situated, would account for not finding them.

The inside of the peduncle (fig. 2 g) was gorged, in the specimen examined by me, with immature ova. The innermost muscular layer consists of longitudinal bundles of unusual size, but placed rather far apart from each other; these do not extend to the very base of the peduncle, and at the upper end they curve inwards, almost to the middle of the under side of the diaphragm, separating the peduncle and capitulum. Outside these longitudinal muscles, there are delicate transverse ones, but apparently there are no oblique muscles in the upper part of the peduncle, as in other Lepadidæ; near the bottom, the transverse muscles form a thicker layer with many of the bundles running in oblique lines.

Mouth.—uLovén has not described this part quite accurately, owing to his not having used high enough magnifying powers. He states that the trophi are soft and functionless, which is far from the case. The whole mouth (fig. 2 d), is unusually small; it is, to a certain extent, probosciformed, and being curved a little downwards, projects slightly over the adductor muscle, to which it is closely placed. The labrum does not project more beyond the general surface of the body, than in many other Cirripedes, but the probosciformed structure is caused by the elongation of the surface fronting the thorax. The summit of the mouth stands above the level of the top of the pedicels of the first pair of cirri. The labrum is slightly hollowed out in the middle of its upper margin; it can scarcely be called bullate, in which it differs from all other Lepadidæ; on the other hand, the outer and inner folds of the labrum are not so close together as in Balanus. On each upper corner, there is, as usual, a small rounded prominence, close to which there is a second slight, rounded, spineless swelling; these latter represent the quite rudimentary Palpi.

The Mandibles (figs. 4, 5) are more highly developed than the other trophi; they are, however, very minute, the toothed edge being only about 16/1000th of an inch in length, measured in its longest direction; the edge is unusually thick, with the teeth placed rather on one side; this organ, when viewed on the labrum side (fig. 5), shows two large teeth placed low down, with the inferior angle pectinated and broadly truncated; but when viewed on the other or maxillæ side (fig. 4), several large and small teeth, placed alternately and irregularly in pairs, are seen extending along the whole edge. The mandibles are furnished, as usual, with three principal sets of muscles attached to the basal fold of the mouth.

The Maxillæ (fig. 7) are still smaller than the mandibles; the spinose edge being only the 1/100th of an inch in length; the edge, instead of being square, and furnished with a double row of long spines, as in all other Cirripedes, is rounded, thick, club-shaped, and with the side facing the mandibles, thinly and irregularly strewed with short, thick, very minute spines; there is a large broad apodeme (a), in the usual place, but it is much more transparent and flexible than common: there are also the usual muscles. In other cirripedes, the mandibles alone seem to force the prey down the œsophagus; but here, the mandibles and maxillæ equally stand over the orifice, and their adjoining spinose faces and edges, seem excellently adapted to force, by their united action, any minute living creature down the passage.

The Outer Maxillæ are almost in as rudimentary a condition as the palpi; they are quite spineless; viewed externally, they appear like two smooth, blunt, very minute projecting points; but viewed internally, the membrane forming the supra-œsophageal hollow seems to be united actually to their tips, so that they do not project at all. I was surprised to find that the longitudinal muscles going to these organs were developed, in proportion to the other muscles, quite as fully as in ordinary cirripedes: hence, these two little outer maxillæ, no doubt, serve as an under lip, and possess the usual backward and forward movement.

The surface of the probosciformed mouth facing the first pair of cirri, has a deep central longitudinal fold, and rather more than half-way down, a transverse fold; just above this latter fold, and therefore quite below the outer maxillæ themselves, the two olfactory orifices are seated; these are unusually large, and the sack into which they lead, is most unusually large and deep. In this Cirripede, I was first enabled to observe that the membrane lining the sack is tubular, and open at the bottom.

Cirri.—There are, as usual, six pair, and not of very small size; they have a shapeless and rudimentary appearance; they are coloured, like the rest of the body, blackish purple: they are quite spineless, and not articulated, but their anterior faces are either obscurely or very plainly lobed, so that in some (for instance in the third pair, Pl. IV, fig. 6), nine or ten prominent steps could be counted, manifestly representing so many segments. The rami are equal in length in the first pair, and slightly unequal in the second and third pair; these two latter are longer than either the first or three posterior pair. There is a small interspace as usual between the first and second pair of cirri. Internally, the cirri are occupied, even up to their tips, by delicate striæ-less muscles. The external membrane of the thorax and limbs, when examined under a very high power, is seen to be covered with minute toothed scales, as in most Cirripedes.

The thorax is articulated as usual: the posterior part, however, is smaller, and tapers more suddenly than in other species, and this corresponds with the smaller size and more rudimentary condition, of the three posterior pair of cirri, compared with the anterior pair. The prosoma is hardly at all developed. The orifice (Pl. IV, fig. 2 e) of the acoustic (?) sack, beneath the first cirrus, is unusually large.

There are no filamentary appendages.

Alimentary Canal.—The membrane lining the œsophagus is unusually thin: it is furnished with the ordinary constrictor muscles, and others radiating from them like spokes of a wheel. The stomach is lined by unusually prominent biliary folds, which in the duodenum are transverse, sending forth, however, short folds at right angles; and these latter, in the proper stomach, become so much developed that the folds appear longitudinal. The rectum extends inwards, about as far as the base of the fourth pair of cirri, but is very short, owing to the little development of the three posterior segments of the thorax. The anus is seated in its usual place, at the dorsal basis of the penis, and is hidden by loose folds of skin; but there are no distinct caudal appendages. The stomach, in the specimen examined, was quite empty.

Reproductive Organ.—The penis (fig. 2, c) is thick, short (about twice as long as the sixth cirrus), constricted at the base, ringed, spineless, with the terminal aperture large; internally it is well furnished with muscles. The two vesiculæ seminales, appeared to be unusually small; and one was much smaller than the other; they do not (I believe) become united into a common tube, till near the apex of the penis. They were empty; and, I presume, from the state of the ova, that their contents had lately been discharged. The whole thorax was filled with a white, fibrous and cellular mass, consisting perhaps of the testes in their undeveloped state. The individual dissected by me, appeared to have been defective in its last act of reproduction, for there were only two or three ova attached to the frænum on one side, and not very many on the other. The ova are much less elongated than is usual; they are of a remarkable size, namely 22/1000ths of an inch in their longer diameter; the membrane by which they are united into a pair of lamellæ is remarkably strong; the frænum (Pl. IV, fig. 2 f) on each side is large, strong, with rounded edges, pale coloured and hence conspicuous; on the side nearest the body, the whole surface is covered with club-shaped glands, having very short footstalks, and being in total length 5/6000ths of an inch; these glands secrete a reticulated layer of gut-formed fibres, attached to the ovigerous lamellæ. In the specimen described by Lovén, the lamellæ (fig. 1, and fig. 2, b, b) appear to have been very large: and in that examined by myself, the peduncle was gorged with immature ova, showing that the female reproductive powers were ample, though at the foregoing period, only a few eggs had been formed.

Habits.—According to Lovén, this species lives imbedded in the skin of Squalus maximus and spinax, in the North Sea: I suspect that it is not closely compressed in its cavity, otherwise, I do not see the use of the two layers of muscles round the whole peduncle; it probably adheres to the sides of the cavity by the tips of the branched, root-like filaments; owing to the flexible nature of the capitulum, this Cirripede can offer little resistance to the water, and, therefore, is little likely to be torn out of its cavity. I have no doubt that it can fold the membrane of the capitulum, like a cloak, round its thorax and cirri; but it certainly can offer far less resistance, than other Cirripedes, to any enemy. This creature must obtain its food, and considering its productiveness much food must be required, in a manner quite different from nearly every other member of its Order. As the whole of the peduncle is imbedded, and as the mouth is probosciformed, with the labrum a little curled over the adductor muscle, I conclude that this Cirripede can reach minute animals crawling by on the surface of the shark's body.

It must be borne in mind that the mouth, as in all Cirripedes, has the power of independent movement, and that the mandibles and maxillæ are here beautifully adapted to catch and force down any small living creature into the muscular œsophagus; the rudimentary outer maxillæ, moreover, no doubt have the power of scraping, like a lip, anything towards these prehensile organs. It will hereafter be seen, that the male of Ibla Cumingii, in which the cirri are quite rudimentary, obtains its food in a somewhat analogous manner, though in this case the whole peduncle moves, and not merely a probosciformed mouth: it deserves attention, that in the male Ibla and in Anelasma, in neither of which the cirri are prehensile, the palpi are rudimentary and useless. I am tempted to believe, that the largely developed olfactory sacks, and perhaps, likewise, acoustic (?) sacks, in Anelasma, replace, by giving notice of the proximity of prey, the loss of tactile cirri. It should be remembered that all Cirripedes subsist on animals which happen to swim or float within reach of the cirri; but here it is only those which happen to crawl within reach of the probosciformed mouth. It would, however, be rash to assert that the cirri in Anelasma, considering their muscular though feeble structure, may not be of some slight use, when thrown over the prey, in preventing its escape.

Professor Steenstrup informs me that, from late observations, it appears that this animal always adheres to the shark's body in pairs. I regret extremely that I have not been able to examine a pair: that the individual examined by me was bisexual, I can hardly doubt, though the male organs certainly were feebly developed; it appears probable, that the individual described by Lovén was likewise bisexual: but after the facts presently to be revealed regarding the sexes in Ibla and Scalpellum, it is quite possible that the male and female organs may be developed in inverse degrees in different and adjoining individuals.

The genus Anelasma is, I think, properly placed between Alepas and Ibla. In several of its characters, such as the absence of calcareous valves, the broad blunt end of the peduncle, the spineless cirri, the small size of the trophi, and more especially the absence of transverse striæ in those muscles, which in mature cirripedes are thus furnished, we see that this genus is in some degree in an embryonic condition.

Genus—Ibla. Pls. IV, V.

Ibla. Leach. Zoolog. Journal. vol. ii, July, 1825.

Anatifa. Cuvier. Mem, pour servir, ... Mollusques, Art. Anatifa, 1817.

Tetralasmis. Cuvier. Regne Animal, 1830.

(Fœm. et Herm.) Valvæ 4, corneæ: pedunculus spinis corneis, persistentibus vestitus.

(Fem. and Herm.) Valves four, horny: peduncle clothed with persistent, horny spines.

Body partly lodged within the peduncle; mandibles with three teeth; maxillæ with two obscure notches; outer maxillæ pointed; olfactory orifices prominent; caudal appendages multiarticulate.

Male and Complemented Male, parasitic within the sack of the female or hermaphrodite; mouth and thorax seated on a long tapering peduncle, but not enclosed within a capitulum; mouth with normal trophi, but palpi small and almost rudimental; cirri rudimental, reduced to two pairs; penis reduced to a pore; caudal appendages rudimentary.

Attached to fixed littoral objects: Eastern Hemisphere.

General Remarks.—As there are only two species as yet known, and as these resemble each other in every respect most closely, a generic description would be a useless repetition of the full details given under Ibla Cumingii. I have taken this latter species as the type, from having, owing to the kindness of Mr. Cuming, better and more numerous specimens. Ibla and Lithotrya are the only two recent genera in which the body of the animal is lodged within the peduncle; but there is no distinction of any importance, though useful for classification, between the capitulum and peduncle; and these two parts, as we have seen, tend to blend together in some species of Conchoderma and Alepas. The entire absence of calcareous matter in the valves and spines of the peduncle, at first appears very remarkable; but we have seen a similar fact in Alepas, and there is an approach to it in some varieties of Conchoderma aurita and C. virgata. In all four valves of Ibla, the umbones, or centres of growth, are at their upper points. The horny spines on the peduncle, are the analogues of the calcareous scales in Scalpellum and Pollicipes; and in this latter genus, two of the species have their scales, almost cylindrical, placed irregularly, with new ones forming over all parts of the surface, and not exclusively at the summit,—in which several respects there is an agreement with Ibla. The shape of the body (i. e. thorax and prosoma, Pl. IV, fig. 8 a´) is peculiar; but it is only a slight exaggeration of what we have seen in several genera, and shall meet again in some species of Scalpellum. The presence of hairs on the outer membrane of the prosoma is a peculiarity confined to this genus amongst the Lepadidæ, though observed in the sessile genus, Chthamalus. The caudal appendages in the I. quadrivalvis attain a greater length than in any other species of the family, being four times the length of the pedicels of the sixth cirrus. A far more important peculiarity is the fact of the œsophagus, in both species, running over or exteriorly to the adductor scutorum muscle, instead of, as in every other species, close under this muscle. I took great pains in ascertaining the truth of this singular anomaly: the course of the œsophagus is approximately represented in Pl. IV, fig. 8 a´ by faint dotted lines. The stomach has no cæca; the biliary folds are longitudinal; there is a marked constriction at the line corresponding with the junction of the thorax and prosoma. There are no filamentary appendages.

The generative system gives the chief interest to this genus. We here first meet with Males and Females distinct; and, within the limits of this same restricted genus, the far more wonderful fact of hermaphrodites, whose masculine efficiency is aided by one or two Complemental Males. The complemental and simple males closely resemble each other, as do the female and hermaphrodite forms; but under the two following species I enter into such full and minute details on these remarkable facts, that I will not here dilate on them. I may add that, at the end of the genus Scalpellum, I give a summary of the facts, and discuss the whole question. The penis (Pl. IV, fig. 9 a) in the hermaphrodite, I. quadrivalvis, is singular, from the length of its unarticulated support, and from the distinctness of the segments in the articulated portion.

As ovigerous fræna occur in the usual place in I. quadrivalvis, though much smaller than in any other species, I have no doubt that they occur in I. Cumingii, although I failed in observing them. The glands on the margin, in I. quadrivalvis, are singular, from not being borne on a long, hair-like footstalk.

Affinities.—Ibla, though externally very different in appearance from Scalpellum, is more nearly related to that genus than to any other; in both genera some species have the sexes separate, the imperfect males being parasitic on the female, and other species are bisexual or hermaphrodite, but aided by parasitic complemental males. In Scalpellum, again, the œsophagus pursues a sinuous course, resembling that in Ibla, though it does not pass exteriorly to the adductor scutorum muscle. The disc of the prehensile antennæ of the larva, in both genera, has an unusual oblong form, like a mule's hoof; there is also an affinity between the two genera in the size and form of the ova, in the prominent orifices of the olfactory cavities, and in the peduncle not being naked; though, in these two latter respects, in the structure of the cirri, and in the multiarticulate caudal appendages, there is an equal affinity to Pollicipes and Lithotrya. I have already shown that Alepas is likewise related to Ibla.

1. Ibla Cumingii. Pl. IV, fig. 8.

I. (fœm.) valvarum marginibus lateralibus, et superficie interiore, cæruleis: pedunculi spinis plerumque annulis cæruleo-fuscis.

Fem.—Valves coloured, along the lateral margins and on the upper interior surface, blue: spines on the peduncle, generally ringed with blueish-brown.

Caudal appendages barely exceeding in length the pedicels of the sixth cirrus: rami of the first cirrus unequal in length by about two segments.

Male,—with scarcely a vestige of a capitulum: maxillæ with fewer spines than in the female.

Hab.—Philippine Archipelago, Island of Guimavas; invariably attached to the peduncle of Pollicipes mitella, in groups of two or three together; Mus. Cuming. Tavoy, British Burmah Empire; Mus. A. Gould of Boston.

FEMALE.

The capitulum is formed of four valves, but is hardly distinct from the peduncle. The latter includes, in its wide upper part, the animal's body. The valves, namely, a pair of scuta and terga, are composed of an extremely hard, horny substance, or properly chitine, and do not contain any calcareous matter; they are extremely flat or thin, and both pairs project freely, like curved horns, to a considerable height above the sack enclosing the body: the terga project about twice as much as the scuta, and their flat apices generally diverge a little. The tips of the valves are frequently broken off; their surfaces are plainly marked or ribbed by the layers of growth, which are wide apart. The bases of the valves externally are hidden by the long spines of the peduncle.

Scuta.—These are shorter and broader than the terga; their internal (Pl. IV, fig. 8 b´) growing or corium-covered surfaces are slightly concave, triangular, with the basal margin longer than the other margins and slightly excised in the middle: there is no depression for the strong adductor muscle: the internal surface of the free horn-like portion, has a small central fold (formed by an oblique crest) running from the summit of the triangular growing surface to the tip of the valve: in perfect specimens, the growing and the free horn-like portions (the latter represented much too long in fig. 8 a´ and b´) are about equal in length: the basal portion of one side of the scutum overlaps the tergum.

Terga.—The internal glowing surface (fig. 8 b´) is almost diamond-shaped, and less in area than the sputa: external surface rounded; internal surface of the free horn-like portion, slightly concave.

Colour and Structure of Valves.—The external surfaces of the scuta and terga are yellow along the middle, plainly marked by zones of growth, and finely ribbed longitudinally: the internal surfaces and sides of the horns of the two valves, are coloured fine blue or purple; in the terga, however, the internal surface is mottled with yellow. In some specimens, especially in one from Tavoy, each zone of growth was only very narrowly edged with blue. When a thin layer is removed from one of the valves, the dark blue or rather purple appears by transmitted light a beautiful pale blue; and it is a very singular fact, that this blue portion is permanently turned by very gentle into a fiery red; the same singular effect is produced by muriatic and acetic acids. This blue part is much harder than the yellow; the latter exhibits, under a high power, a folded structure, and is penetrated by a few tubuli, whereas the harder blue portion has a cellular or scaled appearance. The spines of the peduncle exhibit, in a smaller degree, similar phenomena.

Peduncle.—This, as already remarked, cannot be distinctly separated from the capitulum; it is much compressed; it is composed of unusually thin and delicate membrane, transversely wrinkled and thickly clothed with long cylindrical horns or spines of chitine. These horns (fig. 8 c´) are not the analogues of the spines which are articulated on the external membranes of many Pedunculated and Sessile Cirripedes, but of the calcified scales on the peduncle of Scalpellum and Pollicipes; for they pass through the membrane (the underlying corium being marked by their bases) and are persistent, being added to, like the valves, during each successive period of growth. Their bases are concave, so that a section of the layers of growth exhibits a series of pointed cones, one within another. Each spine is nearly cylindrical, irregularly curled, and nodose or slightly enlarged at intervals: the apex smooth and pointed; the exterior surface longitudinally and finely ribbed, like the valves. The spines increase irregularly in size from the bottom to the top of the peduncle, those at the carinal and rostral ends being generally the longest; they point upwards and hide the bases of the valves. They are not arranged symmetrically, and new ones are formed over all parts of the peduncle. They are formed of the same substance as the valves, and do not contain any calcareous matter. These horns are yellowish, generally ringed with pale and dark blueish brown, which on pressure becomes slightly opalescent with pale blue and fiery red: sometimes only the upper horns are thus ringed, and in rare instances all are simply yellowish. The muscles of the peduncle run up to the bases of the four valves.

Surface of Attachment.—The cement appears to proceed from only two points. In some specimens, a considerable length of one side of the peduncle was fastened to the surface of attachment, the horns or spines being enveloped in the cement. The prehensile antennæ of the larva will presently be described under the male.

The length of an average specimen, including the peduncle and valves, is about half an inch, and the width across the widest part one fifth of an inch. Mr. Cuming has one specimen an inch in length, but this is owing to the peduncle being unusually tapering. In a specimen kept some years in spirits, the cirri, trophi, caudal appendages, and corium under the membrane between the scuta, were all dark purple; the sack and corium of peduncle clouded with purple, and the prosoma pale-coloured.

The Body (Pl. IV, fig. 8 a´) is small compared with the capitulum and peduncle; it is much flattened; the prosoma is of a very peculiar shape, being square, the sides of equal length, and, in an average-sized specimen, 75/1000th of an inch long. The peculiar shape arises from the great distance between the first and second cirrus—from the mouth being far removed from the adductor scutorum muscle—and lastly, from the lower part of the prosoma being not at all protuberant. The thorax which supports the cirri is also unusually small, plainly articulated, and separated from the prosoma by a deep fold. The thin membrane of the prosoma is studded with some fine, pointed hairs, about 3/400ths in length, and articulated on little circular discs.

Mouth, placed at a considerable distance from the adductor, and directed in an unusual manner towards the ventral surface of the thorax: the trophi are arranged, in a curved line, facing the thorax (see Pl. V, fig. 2, for this part in the male), and therefore less laterally than is usual.

Labrum (Pl. IV, fig. 8 a´ opposite c) highly bullate; the upper part produced into a blunt point: on its crest there are no teeth.

Palpi (fig. 8 a´ opposite d) small, blunt and rounded at their ends; inner margins slightly concave.

Mandibles (Pl. X, fig. 4), with three teeth, of which the first is much larger than the second and third, and distant from them: inferior angle produced and pectinated; upper edges of the second and third teeth finely pectinated.

Maxillæ (Pl. X, fig. 11) small, slightly but distinctly indented by two notches, supporting, besides the three upper great spines, three pairs of moderately long spines and some finer ones: apodeme short, thick.

Outer Maxillæ, unusually pointed, with the inner bristles not very numerous, continuously arranged; externally, the bristles are longer. Olfactory orifices, tubular, projecting, flattened, square on the summit, smooth: they point upwards and obliquely towards each other: they arise more laterally than in the other genera, namely outside the bases of the outer maxillæ, and between them and the inner maxillæ.

Between the bases of the first pair of cirri, there is a conical prominence, clothed with bristles and coloured purple: it projects nearly as high as the top of the lower segment of the pedicel of the first cirrus: it lies over the infra-œsophageal ganglion, and serves, I suspect, to fill up a little interval between the outer maxillæ.

Cirri long, little curved: the first pair (Pl. IV, fig. 8 a´) is situated at an extraordinary distance from the second; hence its basal articulation is on a level with the upper articulation of the pedicel of the second cirrus. In the three posterior cirri, the segments are laterally very flat, with their anterior surfaces not protuberant; each supports three pairs of thin, non-serrated bristles, of which the second pair is much shorter than the upper, and the lowest pair minute; between each pair there is a minute, rectangulary projecting bristle; dorsal tufts consist of two or three spines, of which one is longer than the others. The two bristles forming each pair, are not of equal length; for in the rami of each cirrus, the inner row of bristles is much shorter than the outer; and this seems to be connected with the flatness of the whole animal, and the consequent little power of divergence in the rami of the cirri. The first cirrus is rather short, with the rami unequal in length by about two segments: the anterior ramus is shorter and thicker than the other: segments numerous, each clothed with several rows of bristles. The second cirrus has the anterior ramus thicker and more thickly clothed with spines than the posterior ramus; this latter is rather more thickly clothed with spines than are the three posterior cirri; the third cirrus is in all these respects characterised like the second cirrus, but in a lesser degree. The pedicels of the second and third cirri are thickly and irregularly clothed with spines; in the three posterior pairs, the spines are placed in two regular rows, with some minute intermediate spines.

Caudal Appendages (Pl. IV, fig. 8 a´, f), multiarticulate, thin, tapering, in one specimen equalling, in another just exceeding, in length the pedicels of the sixth cirrus. In the latter specimen there were thirteen segments, of which the basal segments were broader and shorter than the upper; these latter are slightly constricted round the middle, so that they resemble, in a small degree, an hour-glass. Their upper margins are surrounded by rings of bristles; the terminal segment being surmounted by one or two very fine bristles much longer than the others. The two appendages are closely approximate; each arises from a narrow elongated slip, attached to the side of the pedicel of the sixth cirrus.

Nervous system.—I examined the upper part of the nervous chord, in order to ascertain whether the infra-œsophagean ganglion, which is of a globulo-oblong shape, was far separated from the second ganglion; and this I found to be the case, in accordance with the distance of the first cirrus from the second. I may here remark, that in S. quadrivalvis I discovered the eye, which, though in all probability really double, appeared to be single; it was situated near to the supra-œsophageal ganglion; and this ganglion was situated near to the adductor scutorum muscle, and at a considerable distance from the labrum. The aperture leading into the acoustic (?) sack, is situated much lower down than is usual (Pl. IV, fig. 8 a´), namely, at the length of the pedicel of the first cirrus beneath its basal articulation.

Generative system.—The specimens here described, of which I examined six, are exclusively female; they have no trace of the external, probosciformed penis, or of the two great vesiculæ seminales, or of the testes: on the other hand, the ovarian tubes within the peduncle are developed in the usual manner, and owing to the large size of the ova, are of large diameter, and hence very distinct: I detected, also, the true ovaria at the upper edge of the stomach.

MALE. Plate V, figs. 1-8.

Of the above-described Ibla Cumingii I dissected six specimens, four from the Philippine Archipelago,[47] and two from the Burmah Empire, and none of them, as we have just seen, possessed the probosciformed penis, the vesiculæ seminales, or the testes, so conspicuous in other Cirripedes; on the other hand, all were furnished with the usual branching ovarian tubes and sometimes with ova, and consequently were unquestionably of the female sex. Within each of these specimens there was attached within the sack, in a nearly central line, at the rostral end, (Pl. IV, fig. 8 a´, h, magnified five times,) a flattened, purplish, worm-like little body, projecting about the 1/20th of an inch: in one of the six individuals, there was a second similar little creature attached at the carinal end of the sack. Before giving the reasons which I think conclusively prove that these little animals are the Males of the ordinary form of the Ibla Cumingii, it will be convenient to describe their structure in detail.

[47] I am deeply indebted to the liberality and kindness of Mr. Cuming, in allowing me to cut up four specimens of this new species; and to Dr. Gould, of Boston, U. S., for the examination of the Burmese specimens.

The whole consists of a long, much flattened peduncle, separated from the mouth and thorax by an oblique fold, (Pl. V, fig. 1 h, b), which is conspicuous on the dorsal margin under the cirri, and can be traced with difficulty to the ventral margin. The thorax, itself rudimentary, and supporting rudimentary cirri, is in some individuals, as in the one represented (fig. 1, magnified 32 times), covered by, or received in the oblique fold h, just mentioned: in other individuals the thorax is drawn out, and then the fold shows merely as a notch on the dorsal margin, and the basal articulations of the cirri stand some little way above it. The basal edge of the large, well-developed month can be traced all round, and on the ventral margin (b), is generally marked by a slight notch. The dimensions and proportions vary much: the longest specimen, including the imbedded portion, was 8/100th, and the shortest barely 5/100ths of an inch in length; the width of the widest portion varied from 1 to 2/100ths of an inch: the specimen figured (Pl. IV, fig. 8 a´, and Pl. V, fig. 1,) is a broad, short individual. Generally, the middle of the peduncle is rather wider than the upper part.

Peduncle.—The main part of the animal, as may be seen in the drawing, consists of the peduncle, of which the imbedded portion tapers more or less suddenly in a very variable manner, and is of variable length,—in one specimen being one fourth of the entire length, and in another consisting of a mere minute blunt point. The free upper part of the animal is bent in various directions, in relation to the imbedded portion. The latter passes obliquely through the chitine membrane and corium, lining the sack of the female, and running along amidst the underlying muscles and inosculating fibrous tissue, is attached to them by cement at the extremity. The peduncle is often, but not in the individual represented, much constricted at the point where it passes through the skin of the female, and generally at several other points, especially towards the extremity (see fig. 1); the stages of its deeper and deeper imbedment being thus marked. The constrictions are, I believe, simply due to the continued growth of the male, whilst the hole through the membrane of the female does not yield. The imbedment, which is considerable only when the lower part of the peduncle is almost parallel to the coats of the sack, seems caused by the growth and repeated exuviations of the female; I believe, that the larva attaches itself to the chitine tunic of the sack, and that the cement, by some unknown means, affects the underlying corium, so that this particular portion of the tunic is not moulted with the adjoining integuments, and that the growth of the surrounding parts subsequently causes this portion to be buried deeper and deeper: it is, I believe, in the same way as the end of the peduncle in Conchoderma aurita, sometimes becomes imbedded in the skin of the whale to which it is attached.

The outer tunic of the peduncle is thin and structureless: in the fold (fig. 1 h) under the cirri, there is a central triangular gusset of still thinner membrane, corresponding in position to the membrane connecting the two terga in the female, and there subjected to much movement. I may here remark, that this fold, in its office of slightly protecting the thorax and in its position, evidently represents the capitulum with its valves, enclosing the whole body of the female. The outer tunic is lined by corium, mottled with purple, and within this there are two layers of striæ-less muscles, transverse and longitudinal, as in all pedunculated Cirripedes. The corium extends some way into the imbedded portion of the peduncle, and consequently, the outer tunic there continues to be added to layer under layer, and as it cannot be periodically moulted, it becomes much thicker than in the upper free part of the animal: the corium, however, does not extend to the extreme point, so that in it growth of all kind ceases.

Antennæ.—The peduncle terminates (Pl. V, fig. 1 e) in the two usual, larval, prehensile antennæ, which it is very difficult to see distinctly; they are tolerably well represented in fig. 5, greatly magnified. Their extreme length, measured from the basal articulation to the tip of the hoof-like disc, is 22/6000ths of an inch, the disc itself being 7/6000ths of an inch. The disc is slightly narrower than the long basal segment, from which it is divided by a broad conspicuous articulation; its lower surface is flat and its upper convex, altogether resembling in shape a mule's hoof; its apex is fuzzy with the finest down; it bears a narrow ultimate segment, thrown, as usual, on one side; this segment supports on its rounded irregular summit, at least five, I believe, judging from the structure of the same part in the male larva of Ibla quadrivalvis, six or seven spines, longer than the segment itself: one long spine arises from the under side of the disc, near the base of the ultimate segment, and points backward: there is also a single curved spine on the outside, near the distal end of the basal segment. These organs were imbedded in a heart-shaped ball or cylinder of brown, transparent, finely laminated cement, and thus attached to the fibrous tissue of the female. The two cement-ducts (fig. 1 f) were very plain, each about 1/6000th of an inch in diameter, containing the usual inner chord of opaque cellular matter. I traced them at the one end into the prehensile antennæ as far as the disc; and at the other, up the peduncle for about one fourth of its length, where I lost them, and could not discover with certainty any cement glands. I may, however, here mention, that I found in the lower half of the peduncle, numerous, yellowish, transparent, excessively minute, pyramidal bodies, with step-formed sides; of these two or three often cohered by their bases like crystals; I have never seen anything like these in other Cirripedes, but it has occurred to me that they may possibly be connected with the formation of the cement: for in the last larval condition of Lepas, the cement-ducts run up to the gut-formed ovaria, filled at this period with yellowish, grape-like, cellular masses, without the intervention of cement glands, and I can imagine that similar masses, not being developed into functional ovaria, might give rise to the yellow pyramidal bodies.

Mouth.—The mouth is well developed; it is represented as seen vertically from above, in Pl. V, fig. 2, magnified about 60 times; the positions of the cirri and the outline of the thorax are accurately shown by dotted lines; a lateral view is given in fig. 1. In the specimen figured, the longitudinal diameter of the mouth, including the labrum, was 5/400th of an inch. The muscles of the several trophi have transverse striæ, and are the strongest and most conspicuous of any in the body. The labrum is largely bullate, with its summit slightly concave; the trophi are arranged in a remarkable manner, in a semicircular line, so as to be opposed to the labrum rather than to each other: there are no teeth or spines on the crest of the labrum, which overhangs the œsophageal cavity.

The Palpi (fig. 2 b and fig. 3) are very small, dark purple, bluntly pointed, with a few small bristles at the point; they do not extend beyond the knob at each corner of the labrum, which is here present, as in all other Lepadidæ; they are much smaller than in the female, though of a similar shape, and consequently, their points are much further apart: within their bases, the lateral muscles of the mandibles are, as usual, attached; they are represented in fig. 3, as seen from the inside, with the eye on a level with the concave summit of the labrum. The rudimentary condition of the palpi is connected, as remarked under the Anelasma squalicola, with the absence of efficient cirri.

The Mandibles (fig. 7) are well developed; they so closely resemble those of the female that it is superfluous to describe them: they are, however, smoother, without any trace of the teeth being pectinated, and with the inferior point smaller: measured in their longer direction, they are 7/2000th of an inch in length, and, therefore, a little less than one third of the size of those of the female. These organs have the usual muscles well developed, and the usual articulations.

The Maxillæ (fig. 8) have a rather rudimentary appearance; yet they have the same size relatively to the mandibles, as in the female, the spinose edge being 3/2000ths of an inch in length. These organs resemble, to a certain extent, those of the female, differing from them in being less prominent,—in the outline being more rounded, with the notches even less distinct,—and in the spines being fewer. The apodeme is short and broad.

The Outer Maxillæ (fig. 6) are pointed, with a small tuft of bristles at the apex; they are much less hairy than in the female, but have nearly the same unusual shape. Outside their bases, and between them and the inner maxillæ, the two well-developed, tubular, flattened, square-topped, olfactory orifices, project in exactly the same remarkable position as in the female; these are not represented in fig. 2, though sometimes they can be very distinctly seen, when the mouth is viewed from vertically above.

Thorax and Cirri.—The thorax is in a rudimentary condition: I did not observe the usual articulations. The whole, as seen from vertically above, is of small size, compared with the mouth; the outline is accurately shown by dotted lines in Tab. 5, fig. 2, together with the positions of the two pair of cirri, the caudal appendages, and anus. The posterior end of the thorax does not rise to the level of the summit of the mouth; and the thorax seems of no service, excepting perhaps as a sort of outer lip to protect the mouth. The cirri are in an extreme state of abortion, and evidently functionless; they are lined with purplish corium, without the vestige of a muscle; they are usually distorted and bent in different directions; they vary in size, and even those on opposite sides of the same individual, sometimes do not correspond, and do not arise from exactly corresponding points of the thorax. There are always two pair of cirri, which, as I conclude from the position of the excretory orifices, answer to the fifth and sixth pair in other Cirripedes. Each cirrus (fig. 4) usually carries only one ramus, placed on a large basal segment, evidently corresponding to the pedicel of a normal cirrus. The posterior are larger than the anterior cirri, which latter spring from points a little lower down on the thorax. In the posterior cirrus figured, the great basal articulation or pedicel, almost equals in length, and much exceeds in thickness, the four segments of the ramus; these segments are furnished on their upper dorsal edges with little brushes of spines, but have not even a trace of the normally larger and far more important anterior spines. In one specimen, the anterior cirrus had a large pedicel, carrying three segments, like those of the posterior pair; but in another specimen, one of the three segments showed traces of being divided into two, thus making four imperfect segments; whilst on the corresponding side of this same individual there were only two ill-formed segments, with their few spines differently arranged. Again, in a third specimen, the great basal segment of the anterior cirrus on one side, bore, exteriorly to the usual ramus, a single segment furnished with bristles, and evidently representing a second ramus; thus showing that the great basal segment certainly answers to a pedicel. I may here add, that on the integuments of these cirri, I observed with a high power, the serrated scale-like appearance common in other Cirripedes. Directly between the bases of the sixth cirrus, there is a very minute papillus, which, under the highest power, can be seen to consist of two closely approximate, flattened points; these, I have no doubt, are the caudal appendages in an extremely rudimentary condition, for I traced the vesiculæ seminales to this exact spot: close outside these rudimentary points, on a slight swelling, is the anus. It will presently be seen that in the male of the closely allied Ibla quadrivalvis, the nature of these caudal appendages admits of no doubt, for in this species they consist of more than one segment, are spinose, and close under them towards the mouth, there is a perfectly distinct papillus, representing the usual probosciformed penis.

Alimentary Canal.—The œsophagus is very narrow, and of remarkable length; from the orifice under the mandibles, it first runs back (in this respect not well represented in Pl. V, fig. 1,) under the bullate labrum, and then straight down the peduncle, where it terminates in the usual bell-shaped expansion, entering one side of the small globular stomach; the latter, at its lower end, is slightly constricted, and then is rather abruptly upturned. The rectum is of unparalleled length, and extremely narrow; it can be best detected after the dissolution by caustic potash of the softer parts, when its inner coat of chitine can be seen to be continuous, in the ordinary manner, with the outer integuments of the thorax. The anus, as already stated, is seated on a slight swelling, and consists of a small longitudinal slit (f, fig. 2), placed close outside the two very minute caudal appendages.

Organ of Sight.—In all the specimens, a little below the fold separating the mouth from the peduncle, and near the abdominal (or rostral) edge, a black ball (c, fig. 1), about 1/1000th of an inch in diameter, is conspicuous. When dissected out, it is somewhat conical in form, and appears to consist of an outer coat, with a layer of pigment-cells of a dark purple colour, surrounding a transparent, rather hard lens, apparently leaving a circular orifice at the summit, and forming a short tube at the base, surrounding what I believe to be a nerve. I was not able to perceive that this eye consisted of two eyes united, which the analogy of other Cirripedes makes me suppose probable, although in the ordinary and hermaphrodite Ibla quadrivalvis, the eye also appeared single. It is seated under the two transparent muscular layers, close upon the upper end of the stomach, and this is the exact position, as stated in the introductory discussion (p. 49), in which the eyes of pedunculated Cirripedes are commonly situated.

Generative System.—Within the muscular layer all round the upper part of the peduncle, and surrounding the stomach, there are numerous, little, rather irregular globular balls, with brown granular centres, so closely resembling the testes in other Cirripedes, though of smaller size, that I cannot doubt that this is their nature: they were much plainer, larger, and more numerous in some specimens than in others. The vesiculæ seminales can seldom be made distinctly out; but having cut one specimen transversely across the thorax, they were as plain as could be desired, lying parallel and close to each other above the rectum, (the animal being in the position as drawn,) and therefore in their normal situation. Each had a diameter four times as great as that of the rectum. In this individual the contents seemed (whether from decomposition or state of development, or from my not having used high enough power, I know not,) merely pulpy; but I have since found, in another specimen, masses of the most distinct spermatozoa, with the usual little knots on them, associated with numerous cells, about as large as and resembling those which I have examined in living Cirripedes, and from which I have every reason to believe the spermatozoa are developed. The vesiculæ seminales unite and terminate under the two extremely minute caudal appendages, and here I think I saw an orifice; but there is certainly no projecting, probosciformed penis.

Having dissected the six specimens with the utmost care, and having scrupulously examined the ovaria in other Cirripedes during their early stages of development, even before the exuviation of the larval locomotive organs, and in specimens of smaller size than the male Ibla, I am prepared to assert that there are no ovaria, and that these little creatures are exclusively males. It should be borne in mind, that in some of the specimens there were perfect spermatozoa in the vesiculæ seminales (as likewise in some of the males of I. quadrivalvis), and, therefore, if these individuals had been hermaphrodites, their ova would have been, at this period, well developed, and ready for impregnation: in this state it is almost impossible that they could have been overlooked. Moreover, it is probable that such ova would not have been very small, for the larvæ whence the parasitic males are derived, attain (as might have been inferred from the known dimensions of their prehensile antennæ, and as we shall show actually is the case in I. quadrivalvis,) the size common amongst ordinary Cirripedia.

Concluding Remarks.—That these animals are true Cirripedes, though having so different an external appearance from others of the class, admits of not the least doubt. The prehensile antennæ, enveloped in cement and including the two cement-ducts, would have been amply sufficient, without other parts—for instance, the mouth, by itself perfectly characteristic with each organ, together with the whole alimentary canal, constructed on the normal plan,—to have proved that they were Cirripedia. Under the head of the closely-allied Ibla quadrivalvis, we shall, moreover, see that the males are developed from larvæ, having every point of structure—the peculiar quasi-bivalve shell, the two compound eyes, the six natatory legs, &c.,—characteristic of the Order. But in some respects, the males are in an embryonic condition, though unquestionably mature, as shown by the spermatozoa;—thus, in the thorax and mouth opening throughout their whole width into the cavity of the peduncle, that is, homologically into the anterior part of the head, and in the viscera being there lodged instead of in the thorax and prosoma, there is a manifest resemblance to the larva in its last stage of development: the absence of a probosciformed penis, the spineless peduncle, the food being obtained without the aid of cirri, and the length of the rectum, are likewise embryonic characters. Not only are these males, as just remarked, Cirripedia; but they manifestly belong to the Pedunculated Family. If a specimen had been brought to me to class, without relation to its sexual characters, I should have placed it, without any hesitation, next to the genus Ibla; if the mouth alone had been brought, I should assuredly have placed it actually in the genus Ibla: for let it be observed how nearly all the parts resemble those of Ibla Cumingii, excepting only in size and in being less hairy. The trophi are arranged in the same peculiar position as in the female; the labrum is largely bullate, without teeth on the crest; the palpi, though relatively smaller, are of the same shape; so are the mandibles; the maxillæ are more rounded and less prominent, but have the same exact size relatively to the mandibles; the outer maxillæ have the same, quite peculiar pointed outline, and the olfactory orifices are tubular, and hold the same unusual position. It is most rare to find so close a resemblance in the parts of the mouth, except in very closely allied genera, and often species of the same natural genus differ more. Again, in the long œsophagus and constricted stomach there is a resemblance to Ibla. In the male of Ibla quadrivalvis, the caudal appendages are multi-articulate; now, this is a character confined to four genera, namely, Ibla, Alepas, Pollicipes, and Lithotrya. I may add, that large tubular olfactory orifices are confined to the same genera, together with Scalpellum. Lastly, it particularly deserves notice, that the prehensile antennæ, in having a hoof-like and pointed disc, with a single spine on the heel, much more closely resemble these organs in Scalpellum, certainly the nearest ally of Ibla, than in any other genus; they differ from the antennæ in Scalpellum, only in the ultimate segment not having a notch on one side. These organs, unfortunately for the sake of comparison, were not found in the female and ordinary form of Ibla. The full importance of the above generic resemblance in the antennæ, will hereafter be more clearly seen, when their classificatory value is shown in the final discussion on the sexual relations of Ibla and Scalpellum.

Here, then, we have a pedunculated Cirripede very much nearer in all its essential characters to Ibla than to any other genus, and exclusively of the male sex; and this Cirripede in six specimens, from two distant localities, adhered to an Ibla exclusively of the female sex. May we not, then, safely conclude that these parasites are the males of the Ibla Cumingii? Considering that, in the same class with the Cirripedia, there is a whole family of crustaceans, the Lerneidæ, in which the males, compared with the females to which they cling, differ as much in appearance as in Ibla, and are even relatively smaller, I should not have added another remark, had there not been under the head of the following species, and of the next genus Scalpellum, a class of allied facts to be advanced, which in some respects support the view here taken, but in others are so remarkable and so hard to be believed, that I will call attention to the alternative, if the above view be rejected. The ordinary Ibla Cumingii must have a male, for that it is not an hermaphrodite can hardly be questioned, seeing how easy it always is to detect the male organs of generation; and we must consequently believe in the visits of a locomotive male, though the existence of a locomotive Cirripede is improbable in the highest degree. Again, as the little animal, considered by me to be the male of I. Cumingii, is exclusively a male, (for there were no traces of ova or ovaria, though the spermatozoa were perfect,) we must believe in a locomotive Cirripede of the opposite sex, though the existence in any class of a female visiting a fixed male is unknown:[48] in short, we should have hypothetically to make two locomotive Cirripedes, which, in all probability, would differ as much from their fixed opposite sexes, as does the Cirripede, considered by me to be the male of I. Cumingii, from the ordinary form. This being the case, I conclude that the evidence is amply sufficient to prove that the little parasitic Cirripede here described, is the male of Ibla Cumingii.

[48] It deserves notice, that in the class Crustacea, both in the Lerneidæ and in the Cirripedia, the males more closely resemble the larvæ, than do the females; whereas amongst insects, as in the case of the glow-worm in Coleoptera, and of certain nocturnal Lepidoptera, it is the female which retains an embryonic character, being worm-like or caterpillar-like, without wings. But in all these cases, the male is more locomotive than the female.

If we look for analogies to the facts here given, we shall find them in the Lerneidæ already alluded to, but in these the males are not permanently attached to the females, only cling, I believe, to them voluntarily. The extraordinary case of the Hectocotyle, originally described as a worm parasitic on certain Cephalopoda, but now shown by Kölliker to be the male of the species to which it is attached, is perhaps more strictly parallel. So again in the entozoic worm, the Heteroura androphora the sexes cohere, but are essentially distinct: "this singular species, however," according to Professor Owen,[49] "offers the transitional grade to that still more extraordinary Entozoon, the Syngamus trachealis, in which the male is organically blended by its caudal extremity with the female, immediately anterior to the slit-shaped aperture of the vulva. By this union a kind of hermaphroditism is produced; but the male apparatus is furnished with its own peculiar nutrient system; and an individual animal is constituted distinct in every respect, save in its terminal confluence with the body of the female. This condition of animal life, which was conceived by Hunter as within the circle of physiological possibilities, has hitherto been exemplified only in the single species of Entozoon, the discovery of the true nature of which, is due to the sagacity and patient research of Dr. C. Th. Von Siebold." In Ibla, the males and females are not organically united, but only permanently and immovably attached to each other. We have in this genus the additional singularity of occasionally two males parasitic on one female.

[49] Cyclopædia of Anatomy and Physiology, p. 142.

I have used the term parasitic, which perhaps ought strictly to be confined to cases where one creature derives its nutriment from another, inasmuch as the male is invariably and permanently attached to and imbedded in the female,—from its being protected by her capitulum, so that its own capitulum is not developed—and from its feeding on minute animals infesting her sack. The male Ibla must seize its prey, guided probably by its well-developed olfactory organs, through the movement of its long, flexible body, furnished with muscles, and with the mouth seated on the summit. We have already seen one instance of a Cirripede, the Anelasma, obtaining its food without the aid of cirri, by means of its probosciformed, flexible mouth. The eye can serve only to announce to the male when the female opens her valves, allowing occasionally some minute prey to enter. In ordinary Cirripedes the penis is long, articulated, and capable of varied movements, I presume for the purpose of impregnating each separate ovum: the male Ibla has no such organ; and no doubt the whole body, furnished like the penis with longitudinal and transverse muscles, serves the same purpose! I may remark, that it seems surprising that so small a male should secrete sufficient semen to impregnate the ova of the female, but the ova are not nearly so numerous in Ibla as in most genera of Cirripedes; and the smallness of the males in some parasitic Crustacea has already been alluded to. The male must always be younger than the female, for the latter must first grow large enough for the larva of the male to crawl into her sack. Whether the male lives as long as the female I know not, but he certainly lives for a considerable period and increases in size, as shown by the depth to which the end of the peduncle is imbedded. Moreover we shall see, under the next species, that the male is metamorphosed from a larva, not one sixth of its own size.

In the male Ibla, abortion has been carried to an extraordinary and, I should think, almost unparalleled extent. Of the twenty-one segments believed to be normally present in every Crustacean, or of the seventeen known to be present in Cirripedes, the three anterior segments are here well developed, forming the peduncle: the mouth consists as usual of three small segments: the succeeding eight segments are represented by the rudimentary and functionless thorax, supporting only two pair of distorted, rudimentary and functionless cirri: the seven segments of the abdomen have disappeared, with the exception of the excessively minute caudal appendages; so that, of the twenty-one normal segments, fifteen are more or less aborted. The state of the cirri is curious, and may be compared to that of the anthers in a semi-double flower; for they are not simply rudimentary in size and function, but they are monstrous, and generally do not even correspond on opposite sides of the same individual. As males in other classes of the animal kingdom often retain some female characters, so here (though the case is not strictly analogous[50]) the male possesses the cementing apparatus, which homologically is part of an ovarian tube modified.

[50] Certain plants offer a closer, though not perfect, analogy. Thus, in the florets of some compositous flowers, the pistil, besides its proper female functional end, serves to brush the pollen off the anthers; while, in the florets of some other compositæ (see the account of Silphium in 'Ch. K. Sprengel Das entdeckte Geheimniss der Natur'), the pistil is functionless for its proper end, the flower being exclusively male, but its style is developed, and still serves as a brush. So in the male Ibla, part of the ovaria, in a modified condition, is still present, and serves as a cementing apparatus.

The individuals in every other genus (with the exception of Scalpellum), in the several families, in the three Orders of Cirripedia, are hermaphrodite or bisexual. Why, then, is Ibla unisexual; yet, becoming, in the most paradoxical manner, from its earliest youth, essentially bisexual? Would food have been deficient, and was the seizure of infusoria by another and differently constructed individual, necessary for the support of the male and female organs? The orifice of the sack of the female is unusually narrow; would the presence of testes and vesiculæ seminales have rendered her thorax and prosoma inconveniently thick? Seeing the analogous facts in the six, differently-constructed species of the allied genus Scalpellum, I infer there must be some profounder and more mysterious final cause.

2. Ibla quadrivalvis. Pl. IV, fig. 9.

Anatifa quadrivalvis. Cuvier. Mém. pour servir ... Mollusq. 1817, Art. Anatifa, Plate, figs. 15, 16.

Ibla cuvieriana. J. E. Gray. Annals of Philosophy, vol. x, New Series, Aug. 1825.

—— ————— J. E. Gray. Spicilegia. Zoolog. Tab. iii, fig. 10.

Tetralasmis hirsutus. Cuvier. Regne Animal, vol. iii, 1830.

Anatifa hirsuta. Quoy et Gaimard. Voyage de l'Astrolabe, Pl. xciii, figæ. 7-10, 1834.

I. (Herm.), valvis et pedunculi spinis sub-flavis: basali tergorum angulo, introrsùm spectanti, hebete, quia margo carinalis inferior longiùs quam margo scutalis prominet.

Hermaph.—Valves and spines on the peduncle yellowish: basal angle of the terga, viewed internally, blunt, owing to the lower carinal margin being more protuberant than the scutal margin.

Caudal appendages four times as long as the pedicels of the sixth cirrus: rami of the first cirrus unequal in length by about six segments.

Complemental Male, with a notched crest on the dorsal surface, forming a rudiment of a capitulum: maxillæ well furnished with spines.