Ormoceras is an actinocerid nautiloid genus and type for the family Ormoceratidae, found in North America from the late Chazyan though the early Cincinnatian of the Middle and Upper Ordovician, but which continued through the Devonian worldwide. Ormoceras contains twelve named species: * O.boreale * O.centrale * O.dobrovljanensis * O.ferecentricum * O.koraiense * O.langskawiense * O.manchuriense * O.nanumforme * O.pollacki * O.schohariae * O.tenuifilum * O.yokoyamai