(da Costa, 1778)
Shell is solid, thick, equivalve and broadly triangular in outline with a round anterior margin but tending to be slightly drawn out posteriorly. Inequilateral, beaks are in front of the midline. Ligament is narrow, exposed, not extensive, reaching one-third of the way to the posterior margin. Lunule is short, heart-shaped, light brown with fine radiating ridges. Escutcheon is elliptical, extensive, reaching almost to the posterior margin; with fine radiating lines. Sculpture of numerous concentric ridges, not normally overlapping each other: in the depressions between each ridge there are fine concentric lines. The concentric ridges are closely packed near the ventral margin. There are three cardinal teeth in each valve and no laterals. Pallial sinus is not deep. Inner margin is crenulate from below the beak forward to the posterior margin of the escutcheon.
Up to 4.5 cm in length.
Dirty white, cream or pale yellow, occasionally polished, usually with three red-brown rays of varying width, radiating from the umbones, these may occasionally merge into each other or break up into irregular linear patterns. Periostracum is thin.
The animal is white and white filaments which fringe the mantle are disposed in tufts. The foot is large and tongue-shaped, adapted in burrowing. Siphons are long and slender and they are united almost throughout.
Inhabits bottoms of clean sand and muddy sand, from above low water-mark to 55 metres.
Very common in the North Sea. It is distributed from the Lofoten Isles, south to the Iberian Peninsula, the Mediterranean and the Black Sea, along the Atlantic coast of Morocco and to Madeira and the Canary Isles (Distr. C. striatula).