This piece is a mystery to me as well as an uncommon fossil from the Mahantango Formation. It's a mold of a large, rambling Bryozoan colony. There is little detail preserved of the exterior save for the internal zooid molds. I have not been able to determine if there are any monticules present which could help with the ID.
I'm thinking this is some sort of Fistulioporid species of Bryozoan but I can't find anything in the literature that would give more of a clue to narrow down the species.
The above specimen was found near Seven Stars, PA in the Mahantango formation, Upper Shale member (Devonian, Givetian stage)