Unionidae,

Unionidae, a family of lamellibranchiate molluscs, whose metropolis appears to be in the western hemisphere, represented in Britain by two genera, Unio and Anodonta. The shell is regular, equivalve, and closed, the ligament external. In Unio the hinge is furnished with teeth. Pearls of a large size and considerable value are often found in U. margaritifera. At Perth an exten- sive fishery flourished in the river Tay until the end of the 18th century, and from 1761 to 1764 produced pearls to the value of £10,000.