Shell patelliform, white, with a posterior, inclined apex and a compressed, subspiral nucleus. Inside porcellaneous, muscle-scar horseshoe-shaped, interrupted over the head. Animal with a plumate gill, at the right side of the head; the right tentacle thickened; two epipodial filaments at the posterior part of the foot. Radula with large rhachidian teeth, cusp wanting or very obsolete, first laterals triangular, followed by 3 smaller, contorted laterals, with distinct cusps, a large cusped fifth lateral, and numerous uncini. The radulae of the species seem to be different from those of similar mollusks, however I think it is nearest allied to Phenacolepas, by the shape of the first lateral; in other respects it differs sufficiently, to make it necessary to establish a new genus. The shells resemble very much those of Cocculina, the only difference, if it prooves to be constant, is that no regular radial sculpture is to be found, as is the case in all the species of Cocculina I have examined. In the species described as Ps. rugosoplicata it is present in some degree, but of a different character, consisting of coarse short striae, quite overwhelmed by the concentric sculpture.