Orthocycloceras

Orthocycloceras, from Ancient Greek ὀρθός (orthós), meaning "straight", κύκλος (kúklos), meaning "circle", and κέρας (kéras), meaning "horn", is an extinct genus of actively mobile carnivorous cephalopods, essentially a nautiloid, that lived in what would be Europe during the Silurian to Devonian from 428.2 to 412.3 mya, existing for approximately 15.9 million years.