Diagnosis with P. cornucopia.—The reddish-orange colour of the valves alone suffices. There is a very slight difference, in the larger proportional size of the upper latera, and in the outline of the basal margin of the carina. In the maxillæ there is, in P. elegans, a greater width between the two upper tufts of fine spines. In the cirri, the segments in the first pair, are more than half as many as those in the sixth pair; in the anterior ramus of the second pair, only 4/15ths of the segments are protuberant and brush-like, whereas in P. cornucopia 5/12ths are in this condition.

3. Pollicipes polymerus. [Pl. VII], [fig. 2.]

Pollicipes polymerus.(!) G.B. Sowerby. Proc. Zool. Soc., 1833, p. 74.

————— Mortoni. (!) Conrad. Journal Acad. Nat. Sci. Philadelphia, vol. vii, p. 261, Pl. xx, fig. 12, 1837.

P. capitulo, valvarum duobus, tribus, aut pluribus sub-rostro verticillis instructo: valvis sub-fuscis: lateribus à supremo ad infimum gradatim quoad magnitudinem positis: carinæ margine basali (introrsùm spectanti) ad medium excavato: pedunculi squamarum verticillis densis, symmetricè dispositis.

Capitulum with two, three, or more whorls of valves under the rostrum: valves brownish: latera regularly graduated in size from the uppermost to the lowest: carina with the basal margin, (viewed internally,) hollowed out in the middle: scales of the peduncle symmetrically arranged in close whorls.

Maxillæ with three tufts of fine bristles, separated by larger spines; caudal appendages uniarticulate; filamentary appendages attached to the prosoma.

Upper California, St. Diego and Barbara, 32° to 35° N., according to Conrad; Mus. Cuming: Low Archipelago, Pacific Ocean; Mus. Coll. of Surgeons: Southern Pacific Ocean, collected during the Antarctic Expedition, Mus. Brit.

Capitulum, but little compressed, broad, with the scuta and terga placed in a more oblique direction, with respect to the peduncle, than is usual, so that the line of orifice forms an unusually small angle with the basal margin of the capitulum. The capitulum is composed of several whorls of valves, which gradually decrease in size from above downwards. In a medium-sized specimen there were four whorls under the rostrum; in the lowest of these whorls, there were between eighty and ninety valves, and in the whole capitulum from one hundred and seventy, to one hundred and eighty. The valves in the lower whorls are not of equal sizes. Viewed externally, the valves seem to touch and overlap each other; viewed internally ([Pl. VII], [fig. 2 a]) they are found to be just separated from each other by transparent membrane; none of the valves are articulated together. The outer surfaces of nearly all the valves, except in the two last formed whorls, are much disintegrated, and seem to be composed of alternate white and brown layers of shell. The membrane connecting the valves, as well as that of the peduncle, (in specimens long kept in spirits,) is brown; but in some dried specimens, there are indications of its having been coloured crimson (as in P. cornucopia), round the orifice and between the valves.

Scuta, irregularly oval, convex, narrow at the upper end; basal margin may be almost said to be formed of three short, unequal margins, corresponding with the rostrum, the rostral and the adjoining latus. The edge corresponding with the latter, is the best marked, and is generally slightly hollowed out, as if a piece had been broken off. The tergo-lateral margin is curved and protuberant. The umbo projects a little over the scutal margin of the terga.