The fossil below is defying my attempts to identify it. It has a rectangular shaped shell with a rounded anterior and posterior. The umbo is near the middle but off center and angled to the anterior end. There are very fine radiating striae (ribs) and concentric growth lines as well. The specimen is about 2cm in length.
All of this leads me to think this is a specimen of Tellinopsis subemarginata. However, most specimens I have seen have the umbo a bit more towards the center of the shell and not angling towards any particular direction. I also don't see a distinct margin from the umbo to the posterior margin. Maybe this is just a representative of the species that is slightly different from the typical form. Maybe it's a juvenile specimen and has not grown enough to show all the features I expect.
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.)