I'm going through some boxes of findings from the Mahantango formation (Devonian, Givetian stage) and came across some decent gastropod fossils that I found at Liverpool, PA.
This is a Cyclonema mold in matrix with a little bit of the exterior shell cast intact. There is also a Nucula varicosa pelecypod just above and to the right of it.
Then there is this mold from the internal chamber of a gastropod. It's tightly coiled and the whorls stack internally rather than rise up like most snails fossils I've seen. It seems to be a fairly wide living chamber and the width of the whorls increases rapidly unlike the Goniatites of the era.