Spines on the upper segments of the posterior cirri, arranged in three or four approximate longitudinal rows, making small brushes. _Habitat._--New Guinea, attached to the spines of a dead Echinus. Brit. Mus., and Cuming. _General Appearance._--Capitulum flat, pear-shaped, placed almost transversely to the peduncle. Valves white, smooth, moderately thick. _Scuta:_ the basal margin, as seen externally, is narrow, and can hardly be separated from the carinal margin; but an internal basal rim, (fig. 5, _b_) (along which the imbedded disc of the carina runs,) shows where, in the other species, the basal and carinal margins are separated. This basal internal rim is not parallel to the external basal margin, but runs upwards to the occludent margin, leaving beneath it a large triangular space, to which the membrane of the peduncle is attached; and this makes it appear as if the rostral umbones of these valves had grown downwards; but, judging from the allied species, _P. fissa_, I have no doubt that the primordial valves really lie on the umbones, and that the growth has been in the usual direction, that is, exclusively upwards. The occludent margin is curved, and blends by a regular sweep into the carinal margin, so that there is no acute upper angle. A distinct line can be seen, as if two calcareous valves had been united, running from the umbo to the upper end of the valve, thus in appearance separating a slip of the occludent margin; internally this appearance is more conspicuous; this structure is important in relation to that of _P. fissa_. The pointed umbones are divergent, and internally under each, there is a large tooth. The two valves are equally convex. _Terga_, entirely absent. The _Carina_ (Tab. II, fig. 5, _a_, _c_), including the disc, is three fourths as long as the scuta; it is placed almost transversely to the longitudinal axis of the peduncle; it is narrow and internally convex; the imbedded disc is very large, forming a continuous curve with the upper part of the carina; this disc runs along the internal basal rim of the scuta, and hence almost separates, internally, the peduncle from the capitulum; it equals one fourth of the total length of the valve, and is thrice as wide as the upper part; it is oval, externally marked by a central line, and with a slight notch at the end, giving a divided appearance to the whole, and indicating how easily a fork might be formed from it. The carina is thick, measured from the inner convex to the exterior surface, which is carinated; heel prominent. _Peduncle_, narrow, very short, not nearly so long as the capitulum.