Gryphaea, common name Devil's toenails, is a genus of extinct oysters, marine bivalve mollusks in the family Gryphaeidae. These fossils range from the Triassic to the Tertiary periods, but are mostly restricted to the Triassic and Jurassic. Both periods belong to the era Mesozoic. They are particularly common in many parts of Britain.These oysters lived on the sea bed in shallow waters, possibly in large colonies.