Gryphaea arcuata

This is one of the 'classics' from Lyme Regis. Nicknamed the 'Devils Toenail' : When fossils could not be explained by orthodox wisdom the locals believed that these were made as the Devil clipped his toenails. They are very numerous and easy to find.
The image below shows four specimens found within a hundred yards of each other on Monmouth Beach just to the west of Lyme. They are all obviously Gryphaea species but seem to vary between the shape of G. arcuata and G. dilobotes. They may, of course, just be variations within a single species.

You usually find just the left valve (the curly bit) without the lid (right valve). I managed to find one and was dissapointed to find that my enthuiasm was not shared by the rest of the party. She was more interested in cider and lardy cake!

A rarer Right Valve