Cadomites is an extinct ammonite

Ammonite

Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...

 genus from the superfamily Stephanocerataceae

Stephanocerataceae

Stephanocerataceae is a superfamily of middle Jurassic ammonoid cephalopods within the order Ammonitida containing diverse forms, generally with sharp ribbing and complex suture lines...

 that lived during the Jurassic Period, which lasted from approximately 200 to 145 million years ago.

Cadomites is directly descended from Stephanoceras

Stephanoceras

Stephanoceras is a Stephanoceratacean genus and type for the Stephanoceratidae, which lived during the Bajocian but is now extinct....

, with a similar collared and lipped aperture rim, but has denser, finer, sharper ribbing. The shell is discoidal, evolute, with a wide umbilicus. The suture is complex.

Cadomites is found in Middle Jurassic

Middle Jurassic

The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....

 (upper Bajocian -lower Callovian) sediments in Europe, Africa, and South Asia.

References

• Treatise on Invertebrate Paleontology
  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, Ammonoidea, -Sephanocerataceae; Geological Society of America, 1957, reprinted 1990.