Shell up to 40 mm in height, oblique, thin, fragile, subequilateral, compressed to inflated, inequivalve, with left valve more convex than right. Valves with commarginal undulations or regular, lamellate ribs and radial ribs or riblets. Auricles unequal, posterior auricles often continuous with disc; anterior auricles distinct. Byssal notch rather deep; ctenolium present.