Going by the fossil example shown on the Pennsylvanian Atlas of Ancient Life, I am calling this find a Pseudorthoceras. The rock was split into two pieces, and the photo is of them joined back up. The white markings are from an air scribe.

Differences between Pseudorthoceras and Mooreoceras, from a local fossil identification plate.

Pseudorthoceras belongs to the class Cephalopoda. Mooreoceras can also be found in the local rocks and could also be what this particular specimen is.