Five genera are described in the Treatise,
Syringonautilus,
Clymenonautilus,
Juvavionautilus,
Oxynautilus, and
Syringoceras.
Syringonautilus and
Syringoceras are known from both the Middle and
Upper Triassic;
Clymenonautilus,
Juvavionautilus, and
Oxynautilus only from the Upper Triassic.
Syringonautilus, which has been found in the Alps, on
Spitsbergen, in India and Japan has a rapidly expanding evolute shell with a perforate
umbilicus and suboval whorl section. The suture has a faint ventral saddle and shallow lateral lobes. The siphuncle is subcentral. The surface is ornamented with fine lirae.
Syringoceras, found in Europe, on the island of
Timur in Indonesia, and in western North America (Calif and Nev) is like
Syringonautilus except that the siphuncle is near marginal.
Clymenonautilus, first of the strictly Upper Triassic genera, is evolute with a perforate umbilicus and deep dorsal impression when the whorl envelops a third of the previous. The whorl section is higher than wide with flattened flanks and rounded ventral and umbilical shoulders. The suture is transverse across the venter and has deep, tongue-like lobes on either side. The inner whorls are covered with fine lirae, and the outer ones are smooth. The position of the siphuncle is unknown.
Clymenoceras comes from Europe.
Juvavionautilus, == Distribution ==