Bivalve oyster shell
This is the commonest type of bivalve from the Upper Greensand of East Devon. You can tell it’s an oyster because the shell is composed of many fine layers built up one on top of the other. Called Exogyra, it would have sat on the sea floor opening its smaller shell (the specimen in the middle shows that side) to filter sea water for food.
Find out more about bivalves on the molluscs pages.