Tienocerasis an extinct orthoceratoid genus from the Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 of China (Hunan

Hunan

' is a province of South-Central China, located to the south of the middle reaches of the Yangtze River and south of Lake Dongting...

). Orthoceratoids are slender conical or near cylindrial, orthoconic, nautiloid cephalopods from the Paleozoic

Paleozoic

The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...

. Nautiloids, which include a number of different extinct orders, were far more divers and numerous in the past, but are represented today by only two closely related genera.

Teinoceras is represented by a smooth orthocone that enlargens slightly with growth and that has a lenticular cross section. The middle of the dorsum and venter (top and bottom) are flattened or depressed and the dorsolateral and ventrolateral areas have longitudinal depressions. Sutures have mid dorsal, mid ventral, and sharp lateral lobes separated by narrow ventrolateral and dorsolateral saddles. The siphuncle

Siphuncle

The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...

, which is small, runs through the middle.

The exact relationship of Tienoceras within the orthoceratoids is unknown.