Gryphaea
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Gryphaea (Lamarck, 1801), also known as Devil's toenails, are a genus of extinct oyster. They are articulate bivalve fossils from the Jurassic period. Gryphaea fossils are common in many parts of Britain.
They lived on the sea bed in shallow waters, possibly in large colonies. Complete Gryphaea fossils consist of a larger gnarly-shaped shell (the "toenail") and a smaller, flattened shell, the "lid". The animal occupied the cavity between the two shells, just like modern oysters. The shells also feature prominent growth bands. The larger, curved shell sat within the mud on the sea floor.
It was thought that carrying one could prevent rheumatism.
Note: 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.
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