Shell resembling that of P. aperta Linné, but flatter, smaller, more quad¬rangular, with a shorter and smaller body whorl, more polished surface, and with an impressed spiral line near the apex which extends to the margin where it marks a slight sinus, behind which the posterior margin is prolonged into a rounded prominent point. The shell is brilliantly polished and smooth except for lines of growth, but near the apex are a few microscopic faint spirals invisible without a lens. Ths spire is wholly immersed and makes in all about one and a half turns. The ventricular plates are formed like those of P. infundibulum, and not like those of P. aperta. The outer surface of the right plate has two longitudinal blackish lines. The two small plates are somewhat more arched than in P. infundibulum. The inner or triturating surface is similar in both. The length of the largest shell observed is 11.5 mm. and its breadth 9.0 mm. The soft parts are in general much the same as in P. aperta, but the cephalic lobe extends farther back and the foot is rounder, flatter, and less rolled up at the sides. As seen from below the body whorl of the shell equals only about one sixth of the total width.
NOT FIGURED

This species is readily distinguished from any other of the group by the posterior point, which, though smaller, recalls that of Chelidonura Adams. The soft parts, however, have no resemblance to the very peculiar, and perhaps partly hypothetical, figure of Quoy and Gaimard. P. amabilis Verrill is much nearer P. aperta, from which, as far as the shell is concerned, it chiefly differs by being a little narrower than the average aperta. The species are, however, quite variable in this respect.

Caribic. Off Dominica. Off Barbados.