A Monograph on the Sub-class Cirripedia Part 9

_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. cra.s.sa_ 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 ac.u.minatis, ovatis; ad pedunculum paene transverse spectantibus; dentibus internis umbonalibus fortibus: tergis nullis: carinae termino basali in disc.u.m 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 c.u.ming.

_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 s.p.a.ce, 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 inters.p.a.ce 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 dest.i.tute 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. cra.s.sa_ and _P. eburnea_ are tied together.

The absence of terga, which are rudimentary in _P. cra.s.sa_, (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. _Aga.s.siz._ 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 s.h.i.+eld, 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 Aga.s.siz'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 inters.p.a.ce 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 s.p.a.ce 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 s.p.a.ce 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.