Cymaceras is a genus within the oppeliid subfamily Ochetoceratinae from the Kimmeridgian stage, around the middle of the Upper Jurassic.[1]
Cymaceras is rather unusual in its wavy keel that leans alternatingly to one side then the other. Shells are involute, compressed, with a narrow venter and distinct inner and outer ribs, both sets of which are curved in a concave forward fashion.