Cheltonia

Cheltonia is an extinct genus of ammonite from the Upper Sinemurian substage of Lower Jurassic of Europe, Africa, and America. It is probably a microconch of genus Oxynoticeras.

Description
Ammonites belonging to this genus had small platyconic shell, on which the last whorl has been eccentrically coiled. Ventral rostrum could be preceded by 3 to 5 crawlings. Umbilicus took about 30—40% of diameter. Ribs were falcoid and weak. Suture has been the same as in the case of young Oxynoticeras.