(Turton, 1822)
Description (shell):
Shell is brittle, globular and equivalve. Inequilateral, umbones bulbous, in the anterior half; most irregular in outline with both ends notched and gaping, and with a posterior dorsal wing formed by the projecting auricle. Sculpture as follows:
1. Anterior lobe with about 20 widely spaced serrated ridges all parallel with the upper margin of the anterior gape.
2. Anterior disc with no more than 12 very fine serrated ridges running obliquely.
3. Median disc, a shallow groove with concentric lines.
4.Posterior disc, with concentric lines, some deeply grooved.
5.Auricle smooth but with a papillate border.
In front of the umbones there is only a short hinge line because the anterior lobe curves abruptly forwards and towards the anterior gape, whilst behind the umbones the auricle is turned upwards and its inner ventral margin appears in a line with the beaks. Interior with a median low groove; dorsal and ventral condyles; an apophysis; the posterior adductor scar large, at the auricle; the anterior small, in front of the umbones.
Pallets with a cylindrical handle about one-third the length of the blade and running into it as a low ridge. The blade is thin, convex outwards, and as wide as it is long, its margins are entire.
Size:
Pallets may reach 12.7 mm in length in large specimens.
Colour:
Exterior, interior and pallets of shell are white.
Distribution:
Not native in the North Sea, but has occurred here in timber from abroad (Distr. T. malleolus). It ranges south to the Atlantic coast of Morocco.