(da Costa, 1778)
Shell roughly wedge-shaped, umbones posterior to midline. Dorsal margin sloping gently anteriorly from umbones, continuous with rounded anterior margin; posteriorly sloping more steeply, posterior margin bluntly pointed. Ventral margin distinctly crenulate, visible from both sides of each valve. Sculpture of fine concentric grooves and numerous fine radiating striations. Growth stages clear. Right valve with two cardinal teeth, the anterior small, the posterior broad and bifid; left valve with two slender cardinal teeth, the anterior weakly bifid. One anterior and two posterior lateral teeth in right valve; single small, anterior and posterior laterals in left valve. Adductor scars, pallial line, and cruciform muscle scars only lightly impressed. Pallial sinus broadly oval, extending to midline of shell (D. vittatus-drawing).
Up to 35 mm.
White, yellowish, light brown, or purple, frequently lighter about the umbones, with pale radiating rays and often with pigmented bands along growth lines. Periostracum light brown to olive-brown, glossy. Inner surfaces glossy, white, often tinted purple, yellow or orange, with growth stages showing as pale bands.
The animal is very agile, of a purplish red or yellow colour; the siphons are pale orange. The mantle edge is fringed; short thick diverging siphons and a very large and pointed sharp-edged foot.
In sand, from the lower shore into the shallow sublittoral.
Distributed from Norway south to the Mediterranean and north-west Africa (Distr. D. vittatus).