An easy pelecypod to ID from the mid Devonian is
Grammysioidea arcuata. It is very oval shaped and has strong concentric ridges that decorate the shell. The umbo is also very pronounced. There is little other decoration to on the shell and this plain look is how you tell it apart from the contemporaneous
Grammysia bisulcata. It doesn't help that their names are similar.
I've found this same species in the
Mahantango formation of Pennsylvania as well.
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.)
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