Gryphaea, one of the genera known as devil's toenails, is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae.

These oysters lived on the sea bed in shallow waters, likely in large colonies.

The soft parts of the animal occupied the cavity between the two shells, just like modern oysters.

A classic location to find these fossils is Redcar, on the northeast coast of England.

The name "devil's toenail" is also used for some fossil species of the genus Exogyra, which is in the same family (Gryphaeidae) as Gryphaea.