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(Pennant, 1777)

Description (shell):
Shell oval, little longer than deep; umbones posterior to midline, conical and prominent. Posterio-ventral margin with a shallow dent: concave on left and convex on right. Sculpture of numerous, fine concentric ridges; growth stages clear. Right valve with two cardinal teeth: anterior small, posterior larger and bifid, with single anterior and posterior laterals; left valve with bifid anterior and slender posterior cardinals and single, small, anterior and posterior lateral teeth. Adductor scars and pallial line clear, pallial sinus broadly oval, extending deep into interior of the shell. Cruciform muscle scars visible close to junction of the pallial line and the pallial sinus (A. crassa-drawing).

Size:
Up to 60 mm long.

Colour:
Off-white or fawn; frequently pale orange or light red about the umbones, with a few irregular rays of red. Inner surfaces glossy, white, tinted with patches of yellow, orange, pink, or purple.

Habitat:
In mixed sandy deposits, from the lower shore, extending far out into shelf waters.

Distribution:
Not common; apparently occurring in the whole North Sea (Distr. A. crassa). Distributed from Norway southwards to Senegal.

Arcopagia crassa