Editing Gryphaea (section)

{{Short description|Genus of molluscs (fossil)}}
{{More citations needed|date=December 2018}}
{{Automatic taxobox
| fossil_range = {{fossil range|199.600|33.900}} [[Sinemurian]] - [[Eocene]]
| image = Gryphaea_arcuata_01.jpg
| image_caption = ''Gryphaea arcuata''
| taxon = Gryphaea
| authority = Lamarck, 1801
}}

'''''Gryphaea''''', one of the genera known as '''devil's toenails''', is a [[genus]] of [[extinct]] [[oyster]]s, [[Marine (ocean)|marine]] [[bivalve]] [[mollusk]]s in the [[family (biology)|family]] [[Gryphaeidae]].

These [[fossil]]s range from the [[Triassic]] period to the middle [[Paleogene]] period{{citation needed|date=November 2021|reason=this last occurrence datum includes extraneous taxa, particularly the Cretaceous Texigryphaea - do any Gryphaea sensu stricto actually occur after the Jurassic?}}, but are mostly restricted to the Triassic and [[Jurassic]]. They are particularly common in many parts of [[the British Isles|Britain]].

These oysters lived on the [[Seabed|sea bed]] in [[Shallow water marine environment|shallow waters]], likely in large colonies. The complete [[fossil]]s consist of two articulated valves: a larger gnarly-shaped shell (the "toenail") and a smaller, flattened shell, the "lid". The soft parts of the animal occupied the cavity between the two shells, just like modern [[Oyster|oysters]]. The shells also feature prominent growth bands. The larger, curved shell sat within the mud on the sea floor. These shells are sometimes found in fossil plates along with ''[[Turritella]]'', [[Clam|clams]], and sometimes [[Shark tooth|sharks' teeth]] and fossilized [[Fish scale|fish scales.]]  Its distribution is common in areas of Europe.

A classic location to find these fossils is [[Redcar]], on the northeast coast of England. There used to be a common folk belief that carrying one of these fossils could prevent [[rheumatism]].

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''.

Two genera have been removed from this genus: ''[[Pycnodonte]]'' and ''[[Texigryphaea]]''.