Orthocycloceras
Orthocycloceras, from Ancient Greek ὀρθός, meaning "straight", κύκλος, meaning "circle", and κέρας, 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.