Trematoceras is an orthoconic

Orthocone

An orthocone is a usually long straight shell of a nautiloid cephalopod. During the 18th and 19th centuries, all shells of this type were named Orthoceras, but it is now known that many groups of nautiloids developed or retained this type of shell....

 nautiloid cephalopod from the Upper Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 of Europe and Asia named by Eichwald in 1851.

Taxonomy

Trematoceras is included in the Michelinoceratinae, a subfamily of the Orthoceratidae

Orthoceratidae

Orthoceratidae, is an extinct family of actively mobile carnivorous cephalapods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, existing for approximately .-Taxonomy:Orthoceratidae was...

Morphology

Trematoceras has a slender, subcylindrical shell with a bluntly pointed apex, long chambers, straight transverse sutures, and a smooth or faintly cancellated surface. The siphuncle is central, tubular, and empty; septal necks short, orthochaonitic; connecting rings cylindrical or only faintly expanded. Chambers contain prominent lamelar mural and episeptal deposits.

Distribution

Trematoceras has been found in Upper Triassic sediments in Afghanistan, Kazakhstan, and the Russian Federation.