Cranocephalites is a Middle Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 (Calovian) ammonitid

Ammonitida

The Ammonitida is an order of more highly evolved ammonoid cephalopods from the Jurassic and Cretaceous time periods, commonly with intricate ammonitic sutures....

genus named by Spath in 1932 and included in the family Cranoceratidae, superfamily Stephanoceratacea.

Cranocephalites, sometimes considered a subgenus of Arctocephalites which has sharply ribbed inner whorls and a smooth outer whorl, has a constricted eccentric body chamber. It is found in middle Jurassic sediments in Alaska, Greenland, Novaya-Zemlya, and eastern Siberia.