This appears to be my first post about a fairly common Pelecypod from the middle Devonian: Nuculites oblongatus. It's an small, oval shaped shell with fine concentric growth lines. The specimen below is an internal cast of the left valve. You can tell by the faint vertical line just to the right of the beak of the shell which is a muscle attachment point. This one comes from the Windom shale or New York.
This specimen was found at a borrow pit on Deep Springs Road in Madison County, NY which exposes the Windom shale member of
the Moscow formation (middle Devonian in age, Givetian stage.)