Aptychen als Kieferelemente der Ammoniten

The jaws of the ammonite generaEleganticeras, Hildoceras, Normannites, Scaphites, Physodoceras, andQuenstedtoceras (ofQuenst. lower jaws only) are described. Lower jaws and aptychi of these genera are shown to be identical. They consist of an inner layer of organic material, which corresponds to the complete anaptychi of liassic ammonites, and an outer layer of calcitic material deposited on both flancs of the lower jaw, giving rise, after decay of the organic layer, to the aptychi. Previously published interpretations of aptychi as opercula or hoods are discussed and rejected. It is concluded that they certainly functioned as jaws or possibly shovel-like devices.