Oppeliidae are compressed to oxyconic, sculptured Haplocerataceae, either unkeeled, unicarinate, bicarinate, or tricarinate; with sutures in great variety, but ribbing usually more or less falcoid or falcate. The Oppeliidae is the principal family of the Haplocerataceae, with the longest durantion, extending from the Middle Jurassic (Bajocian) to the Upper Cretaceous (Cenomanian) Their derivation is from the Hildocerataceae.