Clarkoceras is a genus of breviconic ellesmerocerid cephalopods, one of only two genera known to have crossed from the Late Cambrian, Trempealeauan, into the Early Ordovician, Gasconadian.

Sutures are essentially straight and close spaced indicating very short camerae (chambers).

Septal necks are straight, reaching about halfway back to the previous septum and the connecting rings are thick and layered Clarkoceras was first thought by Clarke to be a pilocerid, who in 1897 give it the name Piloceras newton-winchelli.

Ruedemann in 1905 recognized this as belonging to the Ellesmerocerida and renamed it Clarkoceras newton-winchelli (Clarke), which became the genotype.

In North America Clarkoceras is found in early Lower Ordovician, Gasconadian age shallow marine sediments near Smith Basin, State of New York, the Llano Uplift of Central Texas, and the El Paso Group of the eastern Rocky Mountains of Trans-Pecos Texas and Southern New Mexico.