Update: This is not a monospecific/monotypic genus. Some additional species are recently described in the mid-continent. I will add the references when I get time.

The monospecific genus Pennoceras has a limited range, the Brush Creek and Pine Creek limestones in Pennsylvania and Ohio. These curious members of the Goniatitida have a maximum diameter of only 37 mm. Miller and Unklesbay named these from specimens in the Carnegie Museum. My own specimen below is from Brush Creek limestone in Parks Township and the soft decalcified limestone. The specimen is orange in color.

Pennoceras seamani
CG-0106—Pennoceras seamani.