Shell thin and brittle, elongate, about four times as long as deep; anterior and posterior margins rounded, gaping at both ends. Anterior end distinctly tapered. Umbones low and indistinct, sited about one-third of length from anterior margin; ligament immediately posterior to umbones, situated in middle third of shell. Sculpture of numerous fine concentric lines, with a group of very fine striae radiating from umbones to middle third of ventral margin. Growth stages visible but not conspicuous. Right valve with a single cardinal tooth projecting perpendicularly from hinge line, a single, elongate anterior lateral and a short, peg-like, posterior lateral tooth. Left valve with two elongate, closely spaced, cardinal teeth; a single, elongate, anterior lateral tooth and a single, projecting, posterior lateral tooth, almost as long as cardinals. Adductor scars and pallial line distinct, pallial sinus short, quadrate; cruciform muscle scars unclear.
Up to 12.7 cm.
White or light brown, with a glossy, light olive or yellow periostracum, postero-dorsal section of shell fawn. Inner surfaces white, glossy (P. legumen-drawing).
Pale yellowish, the mantle tinged with red and its edges fringed are not united. The siphons are separate for the greater part of their length and coloured reddish. The purple-red foot is club-chaped when extended (P. legumen-animal).
Burrowing in sand, from the lower shore into the shallow sublittoral.
Off south-west coasts of England, Wales, and Ireland, probably not in the North Sea. Distributed south to the Mediterranean and north-west Africa.