Glycymeris nummaria  Glycymeris nummaria is a species of saltwater clam, a marine bivalve mollusc in the family Glycymerididae, the bittersweet clams. The shell of an adult "Glycymeris nummaria" can be as large as . It is quite thick, almost circular in shape, with a sculpture of radiating striae and fine concentric lines. The surface is dull and may be dark or pale brown, but also whitish-yellowish. Inside of the shell is glossy, white or pale yellow, often with irregular brown markings. This species is widespread from Norway to the Mediterranean Sea. It lives in sandy-muddy gravels offshore to depths of about .