Two cyrtoconic cephalopods are described from the San Andres Limestone [Permian] of New Mexico, Sorinoceras costatum, n. g., n. sp., and Mariceras gracile, n. sp. The family Scyphoceratidae, to which they belong, is revised, and the genera Ventoroceras and Aipoceras removed to the Aipoceratidae Solenochilidae. Problems in evolution and classification are reviewed with particular reference to late Paleozoic Nautiloidea. Recommended is the Rutoceratida with Rutoceratina, Tainoceratina, and Aipoceratina as possible suborders, the Nautilida with Centroceratina, Liroceratina, and Nautilina. Regrettably, evidence of the origin of the Neptunoceratidae, Scyphoceratidae, and Dentoceratidae is yet inconclusive.