Poterioceras curtum is a Pennsylvanian cephalopod first described by Meek & Worthen in 1860. I originally misidentified these as Ctenobactrites isogramma. This is not the first report of this species in Western Pennsylvania. A report from the Annals of the Carnegie Museum in 1947 features specimens from the Brush Creek
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. Pseudorthoceras belongs to the class Cephalopoda.