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. Linnaeus. Syst. Naturae, 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 Linnaeus; but I find it so named in all old collections, and it seems to agree very well with Linnaeus's description. There has been much groundless confusion about this species; I have no hesitation in giving A. striata, of Brugiere, 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 praecipue); scuto dextro dente forti interno umbonali, laevo aut dente exiguo, aut mera crista instructo; margine occludente arcuato, prominente: pedunculi parte superiore aurantiaca.

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, Janthinae, Spirulae; 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 deg., 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 Janthinae and Spirulae 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 deg. to 180 deg.; 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.

—— spirulae (!) (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, crasse sulcatis, saepe pectinatis; scutorum crista prominente ab umbone ad apicem juxta marginem occludentem pertinente: furcae carinalis cruribus inter angulos 135 deg. et 180 deg. 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 deg. to 180 deg.

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, spirulae, 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. spirulae 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 deg. to 180 deg.; 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. Maxillae 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 maxillae 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 maxillae,—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 Paecilasma; 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 maxillae. 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; carinae parte superiore lata, plana, supra furcam valde constricta; furcae 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 Laminariae in the whole Antarctic Ocean: Bass's Straits, Van Diemen's Land: Bay of Islands, New Zealand, lat. 35 deg. S.: lat. 50 deg. S., 172 deg. W.: coast of Patagonia, lat. 45 deg. S.: attached to bottom of H. M. S. Beagle, lat. 50 deg. 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 deg., 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.—Maxillae, 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 deg. 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; carina rectangule flexa, parte inferiore in discum planum oblongum expansa.

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, Spirulae Janthinae, 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, Bacillariae, I thought that this was the case; others have supposed that it consisted of some encrusting algae 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 antennae of the larva, which, as usual, terminate the peduncle. The antennae 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 Velellae, 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. Maxillae 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: vesiculae seminales purple, much convoluted, lying within the prosoma; testes dendritic, scarcely enlarged at their terminal points, purplish; ovigerous fraena 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 Paecilasma 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.

PAECILASMA. 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.

Valvae, 3, 5, aut 7, approximatae: carina solum ad basales apices tergorum extensa, termino basali aut truncato aut in discum profunde infossum producto: scuta paene 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; maxillae 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 maxillae 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. Kaempferi and P. aurantia, which have their carinae 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 maxillae 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 maxillae 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. Kaempferi 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. PAECILASMA KAEMPFERI. Pl. II, Fig. 1.

P. valvis 5; carinae basi truncata et cristata: scutorum dentibus internis umbonalibus fortibus: tergorum acumine basali truncato, margini occludenti paene 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.

Maxillae 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 Kaempferi 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 striae 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. Maxillae 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. PAECILASMA AURANTIA. Pl. II, Fig. 2.

P. valvis 5; carinae basi truncata: scutis ovatis, margine basali perbrevi, dentibus parvis, internis, umbonalibus instructo: tergorum acumine basali peroblique 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.

Maxillae 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. Kaempferi, 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. Kaempferi, 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. Maxillae, with three great upper spines, beneath which there is a deep notch bearing some delicate spines; inferior upraised part, as in P. Kaempferi.

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. Kaempferi, 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 maxillae; 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 Paecilasma, 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. PAECILASMA 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; carinae termino basali in discum parvum infossum producto: scutis convexis, dentibus internis umbonalibus nullis: tergis paene rudimentalibus, vix carina 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. Maxillae, 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. PAECILASMA FISSA. Pl. II, Fig. 4.

P. valvis 7; scuto utroque e duobus juxtapositis segmentis formato; segmento altero intus dentato: tergis brevibus, ter aut quater carina latioribus: carinae 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. Maxillae 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. PAECILASMA 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 paene transverse spectantibus; dentibus internis umbonalibus fortibus: tergis nullis: carinae 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; maxillae (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 caeca; 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 Paecilasma; 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.

Valvae 5, quae fere pro septem haberi possent, scuto in segmenta plane duo, ad angulum autem rostralem conjuncta, diviso: carina plerumque sursum inter terga extensa, deorsum aut disco infosso aut furca aut calyce terminata.

[32] From [Greek: dichelos], 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; maxillae 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 Paecilasma.

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 deg. to 90 deg., 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 fraena, 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. Maxillae 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 maxillae, 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, Paecilasma, 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 Paecilasma 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 Paecilasma 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 Paecilasma; 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 Paecilasma 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 Paecilasma 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 Paecilasma, 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 paulo 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.

Maxillae, 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 maxillae 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 paene dimidia: tergis bipenniformibus, margine crenato, spina postica, 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 deg. 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. Maxillae 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 fere dimidia: 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.