General Appearance and Structure of Shell.—Shell dirty white, pale brown, or gray: conical, moderately depressed: walls either broadly and irregularly folded (fig. [3 a]), with the surface corroded, or (when attached to ships’ bottoms and sometimes to other Cirripedes) narrowly and regularly folded ([3 b]), with the surface well preserved, smooth, and generally covered by thin brown membrane. These latter specimens generally have the shell more steeply conical, with the orifice rather smaller, and the radii broader, than in the first-mentioned specimens, which are attached to coast-rocks and shells, and have had their summits worn down. The sutures in all cases are tolerably distinct, and have their edges toothed and interlocked: the crenations are visible before the compartments are disarticulated, when viewed either internally or externally, but occasionally they are obscure. The radii, when best developed, are rather narrow, and of equal width on both sides of the sutures, with their summits rounded: their surfaces are finely ribbed transversely, each rib corresponding with, or rather forming a point of, the toothed edge. On the under side these teeth usually are a little hollow or are pitted: the radii, in fact, may be said to be folded, like the parietes, only more symmetrically and narrowly, so that the points in the opposed edges interlock. The edges of alæ are serrated, but more finely than the radii. The parietes are rather thin, with their under surfaces generally smooth. The sheath does not descend far down the shell. The colour of the corium lining the sack and the animal’s body varies considerably, being either almost black or pale purple; and the specimens adhering to ships’ bottoms are internally almost white. Of these latter specimens, I have seen some .6 of an inch in basal diameter: of corroded specimens attached to littoral shells, I have not seen one quite .4 of an inch in basal diameter.
Scuta, with the articular ridge very prominent: the pit for the adductor is deep, and there are generally some distinct, though minute, pits for the lateral depressores. The Terga (fig. [3 c]) have the articular ridge very prominent; and the carinal margin is rather more arched and protuberant than in the other species.
Mouth.—The crest of the labrum is toothed: the palpi are short, truncated, with long spines arising from their ends, and along the basal exterior margin. In the mandibles the first tooth is seated rather far from the succeeding teeth: the inferior part is coarsely pectinated: the maxillæ are deeply notched. The tips of second pair of Cirri have many coarsely pectinated spines: the shorter ramus had six segments, whilst the shorter ramus of the third pair had eighteen segments: the segments on the posterior cirri carry five pairs of main spines.
Branchiæ, &c.—These consist of a double fold, the outer one being the largest, and the inner semi-circular, as has been described under the genus. In a young specimen, only one tenth of an inch in basal diameter, the branchiæ consisted of a single fold; in a specimen a little larger, there were two folds, but these were of equal size: ultimately the outer fold increases in size so as to become nearly double the inner fold. The Ovarian tubes are remarkable from their large diameter. I was surprised to observe in the specimen only one tenth of an inch in basal diameter, that the larvæ were ready to escape. On the prosoma, there are some longish hairs arranged in short rows, and some few on the membrane lining the sack, and some on the opercular membrane and valves.
It may be seen in Pl. [18], fig. [3 a], and [3 b], that I have here united two varieties considerably different in external aspect: I have done this without hesitation, inasmuch as there are intermediate forms, and as the differences are analogous with those so commonly occurring in sessile cirripedes; dependent on whether or not the specimens have been exposed to corrosion. I have seen both varieties from Natal, and both from the west coast of Africa; although the smooth, well-preserved, narrowly plicated varieties seem more common in western than in southern Africa. With respect to the range of the species, I have seen a specimen from the West Indies, but it was the variety which so commonly adheres to ships’ bottoms. This variety often arrives alive in British ports; and I have seen a specimen picked up dead on the beach near Dublin.
6. [CHTHAMALUS] HEMBELI. Pl. [18], fig. [5 a]-[5 d], e.
EURAPHIA HEMBELI. Conrad. Journal Acad. Nat. Sc. Philadelphia, vol. 7, 1831, Pl. 20, fig. 6.
Shell dull reddish purple: sutures, when not obliterated, formed by interlocking teeth: basis sometimes rendered calcareous by the inflexion of the parietes: scutum with two or three furrows extending down the middle of the valve.
Hab.—California, near S. Diego, according to Conrad. Mus. Brit., Cuming.