What is "oncoceras"

Oncoceras is an oncocerid genus, family Oncoceratidae from the middle and upper Ordovician of North America and Europe.

The shell, or conch, of Oncoceras is relatively short, a curved, compressed brevicone with a maximum width in the phragmocone just behind the body chamber, narrowing toward the aperture. The siphuncle is small, necks recurved.