Chapter L: ANSERIFERA. Linnæus. Syst. Naturæ, 1767 (2)

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 [Greek: oxunô], to sharpen, and [Greek: aspis], 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.