Large shell almost circular in outline, thin, translucent, somewhat flattened, rather fragile, greatly laterally compressed, lower valve flat, upper valve slightly convex. Outer surface smoothish with 3: prominent finely lamellate concentric growth lines. Inner surface smooth, nacreous, shiny with only very weak radiating lines, round adductor scar at the valve centre; inner antero-dorsal and postero-dorsal margins often slightly rugose. Cardinal teeth 2. forming unequal ridge-like nymps in the right valve, with corresponding grooves in the left valve; posterior ridge distinctly longer than the anterior ridge. Filibranchiate gills. Foot narrow, long, cylindrical. Mantle widely opens ventrally, with marginal tentacles. Hinge line rather straight, short, not raised. Umbones small and inconspicuous. Ligament internal. Colour: exterior silvery white with a dull finish, occasionally with pale brown or light purple umbones.