Gryphaea (Devil's Toenail) Fossil Oyster - Jurassic

This is a fossil oyster (Gryphaea arcuata) more commonly known as the "Devil's Toenail" It comes from the Lower Jurassic deposits near Gloucestershire, Great Britain.

Gryphaea is a genus of extinct oysters that lived in shallow water in large colonies. The complete fossils 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 oysters. There used to be a common folk belief that carrying one of these fossils could prevent rheumatism