Philippi, 1844
Description (shell):
Shell thin, fragile, tumid; broadly oval, with a concave ventral margin, appearing bean-shaped. Umbones subterminal. Periostracum raised into broad fringes of smooth, slender spines, often absent about umbones and anterio-ventral margin. Sculpture of fine concentric lines. Small oval protuberance on hinge line, close to umbones, with series of transverse ridges, visible with hand lens in the largest specimens (M. phaseolina-drawing).
Size:
Up to 20 mm long.
Colour:
Shell light yellow to light purple; periostracum horn, light-brown, or yellow-brown, paler along umbonal ridges. Inside of shell bluish white to light purple.
Habitat:
From lower shore downwards.
Distribution:
Distributed from northern Norway to the Mediterranean and north-west Africa. Absent in the southern North Sea (Distr. M. phaseolina).