_Nervous system._--I examined the upper part of the nervous chord, in order to ascertain whether the infra-oesophagean ganglion, which is of a globulo-oblong shape, was far separated from the second ganglion; and this I found to be the case, in accordance with the distance of the first cirrus from the second. I may here remark, that in _S. quadrivalvis_ I discovered the eye, which, though in all probability really double, appeared to be single; it was situated near to the supra-oesophageal ganglion; and this ganglion was situated near to the adductor scutorum muscle, and at a considerable distance from the labrum. The aperture leading into the acoustic (?) sack, is situated much lower down than is usual (Pl. IV, fig. 8 _a´_), namely, at the length of the pedicel of the first cirrus beneath its basal articulation. _Generative system._--The specimens here described, of which I examined six, are exclusively female; they have no trace of the external, probosciformed penis, or of the two great vesiculæ seminales, or of the testes: on the other hand, the ovarian tubes within the peduncle are developed in the usual manner, and owing to the large size of the ova, are of large diameter, and hence very distinct: I detected, also, the true ovaria at the upper edge of the stomach. MALE. Plate V, figs. 1-8. Of the above-described _Ibla Cumingii_ I dissected six specimens, four from the Philippine Archipelago,[47] and two from the Burmah Empire, and none of them, as we have just seen, possessed the probosciformed penis, the vesiculæ seminales, or the testes, so conspicuous in other Cirripedes; on the other hand, all were furnished with the usual branching ovarian tubes and sometimes with ova, and consequently were unquestionably of the female sex. Within each of these specimens there was attached within the sack, in a nearly central line, at the rostral end, (Pl. IV, fig. 8 _a´_, _h_, magnified five times,) a flattened, purplish, worm-like little body, projecting about the 1/20th of an inch: in one of the six individuals, there was a second similar little creature attached at the carinal end of the sack. Before giving the reasons which I think conclusively prove that these little animals are the Males of the ordinary form of the _Ibla Cumingii_, it will be convenient to describe their structure in detail. [47] I am deeply indebted to the liberality and kindness of Mr. Cuming, in allowing me to cut up four specimens of this new species; and to Dr. Gould, of Boston, U. S., for the examination of the Burmese specimens.