insubrica Right and left valve of the same specimen: The shell of an adult Glycymeris nummaria can be as large as 60 millimetres (2.4 in).

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.

It lives in sandy-muddy gravels offshore to depths of about 100 metres (330 ft).