Frechites is an early Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 ammonite, a kind of cephalopod with an external shell, included in the ceratitid

Ceratitida

The Ceratitida is an order that contains almost all ammonoid cephalopod genera from the Triassic as well as ancestral forms from the Upper Permian, the exception being the phylloceratids which gave rise to the great diversity of post Triassic ammonites....

 family Beyrichitidae.

Taxonomic revision

J.P. Smith, 1932, put Frechites in the Ceratididae where it remained included in the Treatise

Treatise on Invertebrate Paleontology

The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...

Part L. It was later removed to the Beyrichitidae, established by Spath, 1934.

Comparative morphology

The shell of Frechites is robust, involute, and strongly ribbed. The outer whorl embraces most of the inner, leaving a small umbilicus. Short, strong ribs appear along the umbilical shoulder that split in twos and threes in the middle of the sides, which continue to the outer, or ventrolateral, shoulder but do not cross the venter, or outer rim, which is left smooth.

The suture of Frechites is partly ammonitic, with a slightly serrate first lateral saddle. The other saddles in the suture are rounded and smooth. As such this is intermediate between common Ceratitidae with entirely ceratite sutures -smooth saddes, serrate lobes, and the normal Beyrichideae with sutures that tend to be ammonitic or subammonitid, with deep serrated lobes and high serrated saddles.

References

• Frechites -Paleobio
• Treatise on Invertebrate Paleontology, Part L, 1957. Geological Society of America and University Kansas Press.
• J.P. Smith, 1932. Lower Triassic Ammonoids of North America. U.S. Geological Survey Professional Paper 167.