General Remarks.—Four of the five species, forming this genus, though certainly distinct, are closely allied. I have already shown, that although the characters separating Lepas, Pæcilasma, and Dichelaspis are not very important, yet if they be neglected these three natural little groups must be confounded together. Dichelaspis is much more closely united to Pæcilasma than to Lepas, and, as far as the more important characters of the animal’s body are concerned, there is no important difference between them. Consequently, I at first united Pæcilasma and Dichelaspis, but the latter forms so natural a genus, and is so easily distinguished externally, that I have thought it a pity to sacrifice it. The carina, (which seems to afford better characters than the other valves in Dichelaspis,) from generally running up between the terga and in ending downwards, in three of the species, in a deeply notched disc or fork, more resembles that in Lepas than in Pæcilasma; in the manner, however, in which the imbedded disc, in D. Warwickii and D. Grayii, nearly cuts off the inside of the capitulum from the peduncle, there is a resemblance to [Pæcilasma eburnea]. In the extent to which the valves are separated from each other, in the bilobed form of the scuta, (the two segments in Dichelaspis, perhaps, answering to the upper and lateral projections in the scuta of [Conchoderma virgata],) and in the basal half of the scuta not descending to the base of the capitulum, there is a considerable resemblance to Conchoderma; in both genera the adductor muscle is attached under the umbones of the scuta; but the structure of the mouth and cirri and caudal appendages shows that the affinity is not stronger to Conchoderma than to Lepas. It appears at first probable, that Dichelaspis would present a much closer affinity to [Pæcilasma fissa], in which, owing to the scuta being formed of two segments, there are seven valves, than to any other species of that genus; but in P. fissa the primordial valve is triangular and is situated on the basal segment, whereas, in Dichelaspis, it is elliptic and is seated between the two segments, and is more in connection with the occludent than with the basal segment; and this I cannot but think is an important difference: in other respects, P. fissa shows no more affinity to Dichelaspis than do the other species of the genus. Finally, I may add that Dichelaspis bears nearly the same relation to Pæcilasma, as Conchoderma does to Lepas.

1. [Dichelaspis Warwickii]. [Pl. II], [figs. 6, 6 a, b].

Octolasmis Warwickii. J. E. Gray. Annals of Philosophy, vol. x, p. 100, 1825; Spicilegia Zoologica. t. vi, fig. 16, 1830.

D. scutorum segmento basali duplo latiore quam segmentum occludens: tergorum parte inferiore paulò latiore quam occludens scutorum segmentum.

Scuta, with the basal segment twice as wide as the occludent segment; terga, with the lower part slightly wider than the occludent segment of the scuta.

Mandibles, generally with four teeth.

Off Borneo, attached to a crab (Belcher): China Sea. British Museum.

General Appearance.—Capitulum much compressed, elongated, with the valves not very close together, the carina being separated by a rather wide space from the scuta and terga. Valves variable in shape, very thin and translucent, covered by thin membrane, which, over the whole capitulum, is studded with minute blunt points.

Scuta.—Segments without internal teeth or an internal basal rim; the occludent segment long, narrow, pointed, not quite flat, sometimes slightly wider in the upper part; about one third of its own length longer than the basal segment; occludent margin slightly arched; basal segment about twice as wide as the occludent segment, triangular, slightly convex; in young specimens ([Pl. II], [fig. 6 b]), the carinal margin of the basal segment is protuberant, and the occludent margin hollowed out; in old specimens the occludent margin of the basal segment is straight, and the carinal margin much hollowed out. In very young specimens the basal segment is very small compared to the occludent.

Terga, variable in shape; flat, lower part wider than the occludent segment of the scuta; occludent margin double, forming a considerable rectangular projection, as in the terga of Lepas; scutal margin deeply excised at a point corresponding with the apex of the scuta, a flat tooth or projection being thus formed; there is sometimes a second tooth ([fig. 6 b]) a little above the basal point. The terga, in the first variety, somewhat resemble in shape the scuta of [Conchoderma aurita].