Help identifying a shell for a total novice

[paul monfils]

In bivalve molluscs the two valves (the two halves of the shell) are usually held together by a fibrous band called the hinge ligament, located at or near the hinge. Once the animal dies and the muscles and other soft tissues decompose, the ligament is the only thing holding the two valves together. In some bivalve families the ligament is quite large and tough, and therefore it is common to find paired shells on the beach. In other families the ligament is rather thin and fragile, and easily broken when the shell is tossed around in the surf, so matched pairs are quite uncommon on the beach. In tellins the ligament is moderately thin, so matched pairs are usually not too common on the beach, though it is not unusual to find a few. When large numbers of paired bivalves are on the beach it is usually an indication that they were thrown up onto the beach alive by heavy surf during a storm, died there from the heat of the sun, and the soft parts were then eaten by birds, crabs, etc.