Bivalve oyster shell
This is an unusually well-preserved example of the very common bivalve, Lopha, a type of oyster. Both shells are articulated together as they would have been in life. To feed, the animal would relax the big muscle holding these shells together allowing them to spring open on a hinge. This created a small gap through which water could be drawn in, filtered for food and then expelled. Look closely and you can see a second specimen on the right-hand side; very often these shells grew in huge piles, one on top of the other.
Find out more about bivalves on the molluscs pages.