Shell rather thin and brittle; markedly eccentric: anterior margin shallowly convex, forming sharp junction with hinge line, posterior margin continuous with hinge line, sloping steeply from umbones. About 24 ribs, with closely spaced concentric corrugations, forming small, flattened scales on ribs. Growth stages distinct. Each valve with two small cardinal teeth; right valve with two anterior and two posterior laterals, left valve with single anterior and posterior laterals. On inner surfaces ribs visible as distinct grooves throughout whole of shell, extending beneath umbones. Posterior margin not crenulate (C. lamarcki-drawing).
Up to 50 mm long.
Off-white, yellowish, or greenish, with darker brown areas, overlain by a greenish-brown periostracum. Inner surfaces dull white or brown.
The gills are long and much folded back, the siphons are rather long, the foot large, long and cylindrical, the mantle margins jagged.
In brackish water.
Overlaps the distribution of Cerastoderma edule. Known positively only from the southern parts of the North Sea and Norwegian coast, but probably present elsewhere (Distr. C. lamarcki). Recorded from many parts of western Europe, the Mediterranean, and the Black Sea.