| Diagnosis |
Shell variable, irregularly rounded in outline, with height about equal to length. Dorsal margin straight and relatively short, not expanded posteriorly in a wing-like ear. Anterior margin sharply sinuous dorsally, ventrally strongly convex and extending well forward of umbones. Posterior margin slightly concave, forming an obsolete angulation with the rounded ventral margin. Umbones small, pointing at anterior end of dorsal margin. Outer surface covered with concentric lamellar processes, with very low radial ridge ending at posteroventral angulation. Ligamental area with a dozen transverse grooves. Nacreous area of the inner side of shell surrounded by a broad, non-nacreous margin. Colour: outside of shell horny to purplish brown. Interior nacreous, with a broad dark brown margin. |
