Terga, large, oval, basal angle broad, square; lower part of carinal margin straight, upper part narrowed in; the apex is covered with membrane and projects freely.
Carina, triangular, internally deeply concave, either straight, and with the apex free, or inwardly and considerably curved; basal margin nearly straight.
Rostrum, about half the length of the carina; either straight or inwardly curved; it projects freely for full half its length; inner growing surface triangular, more than twice as high as wide; basal margin very slightly hollowed out. The sub-carina and sub-rostrum are larger than the largest of the latera; their inner surfaces are transversely elongated, rounded at both ends, and slightly concave; externally they are pointed, and project outwards; sometimes the sub-carina, and sometimes the sub-rostrum is the largest.
Latera, small, with their inner surfaces transversely elongated, the larger being the most elongated. Externally they are acuminated, and directed upwards; they project but very little beyond the thick membrane in which they are imbedded. Neither the number, size, nor shape of the latera agree on opposite sides of the same individual; and it would appear that, occasionally, some of them cease to grow, and disappear. In the large specimen with only thirty-one valves, the three pairs of latera, corresponding to the upper, rostral, and carinal latera in Scalpellum, were larger in a marked manner than the others; but in the specimen with fifty-four valves, this could hardly be said to be the case. In this latter specimen, some of the valves in the lowermost whorl were exceedingly minute.
Peduncle, broad, about as long as the capitulum; surface of attachment wide; calcareous scales minute, placed in transverse rows, which become less and less regular in the lower part. The scales do not stand very close together; they are of unequal sizes and irregular outline; generally spindle-shaped; calcareous matter is added regularly only to the scales in the uppermost row, and irregularly to some of the lower scales. The latter, consequently, are the largest, and often much elongated; they are sometimes of singular and irregular shapes.
Colour.—The membrane covering the valves and forming the peduncle, (after having been long kept dry, and not having been in spirits,) is dark reddish chocolate-brown; corium of sack dark purple; cirri banded with dark purplish-brown, with the lower parts of the trophi similarly coloured.
Filamentary Appendages, none, but on the prosoma there are scattered some small papillæ, which are roughened by finely spinose scales, like combs; these papillæ certainly seem to represent the filaments in Pollicipes cornucopia and its two allies.
Ovigerous Fræna, seated in the same position as in P. spinosus, but rather longer, with an elliptical tuft of glands on the crest.
Mouth, not placed far from the adductor muscle.
Labrum, moderately bullate, with the upper part not overhanging; no teeth on the crest. Palpi, short, broad, blunt.