Acleistoceratidae
The Acleistoceratidae is a family of oncocerids that contains genera characterized by depressed exogastric brevicones and cyrtocones that range from the Middle Silurian to the Middle Devonian. The siphuncle is broadly expanded, and in some actinosiphonate.
The Acleistoceratidae are derived from Oncoceras through Amphycertoceras, independently of the Oonoceras stock. The family is named for the genus Acleistoceras. All told some 22 genera have been described.