(Philippi, 1836)
Description (shell):
Shell obliquely oval, thin and fragile. Sculpture of 28 or more broad ribs, with indistinct concentric ridges between. Each rib with numerous small, closely spaced, flattened spines, present over whole of shell although sometimes worn on greatest areas of curvature. Growth stages indistinct. Each valve with two small cardinal teeth; right valve with two anterior and one posterior lateral teeth, left valve with single anterior and posterior teeth, the anterior being the largest. Adductor scars clear, pallial line broad and ill-defined; external sculpture visible on inner surfaces as grooves extending throughout whole of shell.
Size:
Up to 12 mm in length.
Colour:
Yellowish white, periostracum thin and indistinct. Inner surfaces white.
Habitat:
In mud, sand, and fine gravel, offshore to about 160 m.
Distribution:
Ranging from Iceland to the Mediterranean and north-west Africa, not in the southern North Sea (Distr. P. minimum).