(Pennant, 1777)
Description (shell):
Shell thin and brittle, obliquely oval, umbones anterior to midline; anterior margin deeply concave about a broad, oval pedal gape. Both valves strongly convex. Sculpture of numerous corrugated concentrated lines and radiating ribs, forming short, triangular tubercles where they intersect, most numerous and pronounced anteriorly. Umbonal reflections without septa. An elongate, lanceolate protoplax dorsally (B. parva-drawing). Apophysis delicate, flat, extending half-way towards ventral margin. Adductor scars and pallial line distinct, pallial sinus rather irregular.
Size:
Up to 50 mm long.
Colour:
Dull white, periostracum yellowish, often discoloured. Inner surfaces white.
Habitat:
Bores into soft limestones, sandstones and argillaceous rocks; lower shore and shallow sublittoral.
Distribution:
Distributed from the southern North Sea southwards to the Mediterranean (Distr. B. parva).