_Mouth._--Labrum moderately bullate, with the lower part more or less produced; crest with blunt, bead-like teeth, and short hairs. _Palpi_ (Pl. X, fig. 8), acuminated and narrow to an unusual degree. _Mandibles_, with two or three teeth, and the inferior angle acuminated; the lateral bristles unusually strong, so as to give the main teeth the _appearance_ of being pectinated. _Maxillæ_, widely notched, with three great upper spines; the part beneath the notch projecting, and either straight or irregular. _Outer Maxillæ_, with the inner bristles either continuous or divided into two groups: exteriorly there is a smaller or larger prominence, with long bristles. The olfactory orifices are either slightly, or not at all protuberant. _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 oesophagus 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.