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

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

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

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

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

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

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

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

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

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