Oxycerites is an extinct ammonoid cephalopod belonging to the haploceratacean

Haplocerataceae

Haplocerataceae is a superfamily of ammonoid cephalopods belonging to the Ammonitida that unites three families, the Strigoceratidae, Oppeliidae, and Haploceratidae, listed below....

 family, Oppeliidae

Oppeliidae

Oppeliidae are compressed to oxyconic, sculptured Haplocerataceae, either unkeeled, unicarinate, bicarinate, or tricarinate; with sutures in great variety, but ribbing usually more or less falcoid or falcate...

, that lived during the middle of the 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...

 Period, between 164 and 160 million years ago

Shells of Oxycerites are involute, compressed and generally smooth with a sharply rounded venter on the outer rim, deeply impressed dorsum on the inner rim, and a small umbilicus.
The living chamber takes up slightly more than half a whorl. Oxycerites grew to a diameter of at least 17.5 cm, about 7 inches.

Oppelia

Oppelia

Oppelia is a haploceratcean ammonite and type genus for the Oppeliidae that lived during the Middle Jurassic between 170 and 164 million years ago. Shells of Oppelia are involute with a small to moderate size umbilicus, bluntly rounded to sharp venter, and deeply impressed dorsum. Sides are...

and Oecotraustes

Oecotraustes

Oecotraustes is an extinct genus from a well known subclass of fossil cephalopods, the ammonites. It lived during the Jurassic Period, which lasted from approximately 200 to 145 million years ago....

are similar and closely related forms. Oppelia is smoother, Oecotraustes more strongly ribbed