_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.
_Maxillae_ 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 Maxillae_, 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. _Linnaeus._ Systema Naturae, 1767.
BRANTA. _Oken._ Lehrbuch der Naturgeschichte, Th. 2, p. 362, 1815.
MALACOTTA et SENOc.l.i.tA. _Schumacher._ Essai d"un Nouveau Syst. des Habitations des Vers., 1817.
OTION et CINERAS. _Leach._ Journal de Phys., vol. lx.x.xv, 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 t.i.tle 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.
_Valvae 2 ad 5, minutae, inter se remotae: scuta bi-aut tri-lobata, umbonibus in medio marginis occludentis positis: carina arcuata, terminis utrinque paene 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; maxillae step-formed; caudal appendages, none.
_Distribution._--Mundane, throughout the equatorial, temperate, and cold seas; attached to floating objects, living or inorganic.
The _Capitulum_ is formed of smooth membrane, including five small valves, of which the terga and carina are often quite rudimentary or absent. Valves minute, thin, generally more or less linear, placed far distant from each other; sometimes imperfectly calcified and covered by chitine membrane, or imbedded in it. The umbones of the valves (together with the primordial valves) are nearly central, so that they are added to at their upper and lower ends; hence their manner of growth is considerably different from that of the valves in Lepas. The adductor muscle is attached to a slight concavity on the under side of each scutum, at the point whence the lobes diverge.
The _Terga_ are placed almost transversely to the scuta; at their lower ends, there is either a very slight prominence in the capitulum, or there is a large tubular, folded appendage, opening into the sack, and apparently serving for respiratory purposes.
_Peduncle_, smooth, moderately long; attachment effected by the cement-stuff being poured out exclusively, as it appears, from the larval antennae. These antennae in _C. aurita_ and _C. virgata_, resemble, in the form of the disc and in the long feathered spines on the ultimate segment, those in Lepas.
The _Filamentary Appendages_ are highly developed; there are six or seven on each side; two are attached beneath the basal articulation of the first cirrus (as is usual in Lepas), and near them there are one or two small pap-formed projections of apparently similar nature; the rest of the filaments are attached to the posterior edges low down, on the lower segments of the pedicels of the cirri. I believe, in all cases, these appendages are occupied by testes.
_Prosoma_, moderately developed.
_Mouth_, situated not far from the adductor muscle; labrum considerably bullate, with the crest hairy and pectinated with inwardly pointing, approximate, flattened teeth: inner fold of the supra-oesophageal cavity slightly thickened and yellowish, villose on the sides.
_Palpi_ of the usual shape, not meeting, moderately broad.
_Mandibles_, with five teeth, graduated in size, nearly equidistant, finely pectinated either on one or both sides towards their bases; inferior angle narrow, either produced into a fine tooth, or almost rudimentary.
_Maxillae_, about 3/4ths of the size of the mandibles, step-formed, with five steps generally distinct; at the upper angle there are two large unequal spines, of which the lower one is the largest, with a third long thin one on the first step; lower spines doubly serrated. Apodeme directed inwards and backwards.
_Outer Maxillae_ (Pl. X, fig. 16) simply arched; the membrane of the supra-oesophageal cavity under these maxillae is highly bullate and villose. Olfactory orifices not prominent.
_Cirri._--First pair not seated far distant from the second pair. The three posterior pair have the anterior faces of their segments considerably protuberant, supporting four or five pairs of long bristles; between which, there is a row of minute, fine, upwardly pointing bristles: on the lateral upper margins of each segment, there are a few very minute spines; dorsal tuft short, with thick and thin spines intermingled. In the first cirrus (of which the rami are nearly equal in length), and in the anterior ramus of the second cirrus, the faces of the segments are highly protuberant, and clothed with thick transverse rows of finely and doubly serrated spines: the anterior ramus of the second cirrus is considerably thicker than the posterior ramus, which latter, together with both rami of the third cirrus, differ from the three posterior cirri only in the intermediate and in the lateral marginal spines being slightly more developed.
_Caudal Appendages_, absent.
_Alimentary Ca.n.a.l._--The upper part of the stomach has four large caeca, of which the posterior one is the largest; the whole surface, also, is covered with minute pits, arranged in transverse rows.
_Generative System_, developed to an extraordinary degree. The testes run into all the filamentary appendages, as well as more or less, into the pedicels of the cirri: the two vesiculae seminales unite _within_ the p.e.n.i.s, either just beyond its basal constriction, or up one third of its length. p.e.n.i.s short, hairy. The ovarian tubes not only fill the peduncle, but extend in a thin sheet between the two folds of corium all round the sack, close up to the terga. The two ovigerous fraena are present in the usual position; the ovigerous lamellae either form several layers, in pairs, one under the other, or are united in a single large cup-formed sheet enclosing the whole animal.
_Colours._--The prevailing tint is a dark purplish-brown, which forms, or tends to form, broad longitudinal bands on the peduncle and capitulum.
_General Remarks._--This genus is intimately related, as has been remarked by Professor Macgillivray,[36] to Lepas: if we look to the body of the animal, which from being less exposed to external influences must, in the Cirripedia, offer the most trustworthy characters, we find that in Conchoderma there are additional filamentary appendages attached to the cirri, that there are no caudal appendages, that the teeth of the mandibles are finely pectinated, and that the ovarian tubes run higher up round the sack; in every other respect, there is the closest similarity, even to the arrangement of the bristles on the cirri. In the capitulum, the difference consists chiefly, though not exclusively, in the less development of the valves, and their consequent wide separation: the scuta, however, in Conchoderma, are added to beneath their umbones, or original centres of growth, which is never the case, or only to a very slight degree, in Lepas. Conchoderma has no very close affinity to any other genus. As the majority of authors have ranked the two common species under two distinct genera (Otion and Cineras), I may observe, that there is no good ground for this separation; in the above few specified points in which Conchoderma differs from the genus most closely allied to it, the two species essentially agree together. If we take the nearest varieties of _C. virgata_ and _C. aurita_, there is but a very slight difference even in the form of their valves, and these hold the same relative positions to each other; the carina, however, is always less developed in _C. aurita_; even the colouring in both tends to follow the same arrangement. The only obvious distinction between the two species, are the ear-like appendages of _C. aurita_, which, however, are not developed in its early age, are subject to considerable variation, are of no high functional signification, and are indicated in _C. virgata_ by two prominences on the same exact spots. On these grounds I conclude, that the generic separation of the two species is quite inadmissible.
[36] Remarks on the Cirripedia, &c.; "Edin. New Phil. Journal,"
vol. x.x.xix, p. 171.
1. CONCHODERMA AURITA. Pl. III, fig. 4.
LEPAS AURITA. _Linn._[37] Systema Naturae, 1767.
OTION CUVIERa.n.u.s (!) BLAINVILLIa.n.u.s (!) BELLIa.n.u.s (!) DUMERILLIa.n.u.s (!) RISSOa.n.u.s. _Leach._ Encyclop. Brit., vol.
iii, Supp., 1824, and Zoological Journal, vol. ii, p. 208, July 1825.
OTION DEPRESSA et SACCUTIFERA. _Coates._ Journal Acad. Nat. Sci.
of Philadelphia, vol. vi, p. 132, 1829.
OTION AURITUS. _Macgillivray._ Edinburgh New Phil. Journal, vol.
x.x.xviii, 1845.
LEPAS LEPORINA. _Poli._ Test. utriusq. Sicil., pl. vi, fig. 21, 1795.
LEPAS CORNUTA. _Montagu._ Linn. Trans., vol. xi, p. 179, 1815.
CONCHODERMA AURITUM et LEPORINUM. _Olfers._ Magaz. der Gesell.
Freunde zu Berlin, 3d Quartel., p. 177, 1814.
BRANTA AURITA. _Oken._ Lehrbuch der Naturgesch., Th. 11, p. 362, 1815.