Pachydesmoceras

Pachydesmoceras is a genus of ammonites belonging to the family Desmoceratidae.
Species of this genus were fast-moving nektonic carnivorous shelled cephalopods. 
They lived during the Cretaceous, from the Albian (112.0-99.6 Mya) to the Santonian (85.8-83.5 Mya) stage.
Distribution.
Cretaceous of Antarctica, Cameroon, India, Japan, Nigeria, Romania, United States (California).