Sp. Chars.— Shell ovato-elliptical, or suborbicular, slightly convex in the median line, Flattended towards the margin; ears small, pointed, depressed, tringular, subequal, conate, their apices elevated above the level of the general periphery of the shell, both separated from the body of the shell, with their outer edges convex; umbones simple, straight, and pointed; muscular impression large, and situated near the beaks and posterior margin; shell thin and delicate; surface ornamented with numberous close, fine, concentric lines.