Cape May, NJ ark shell or cockle?

[paul monfils]

This is not an ark shell, but a cockle, family Cardiidae. Not Dinocardium robustum, possibly Trachycardium muricatum. In any case, it is not a species normally found in your locality, so someone may have purchased it in a bag of shells at a tourist shop, and dropped it where you found it. In which case it could also be a Pacific species.