Tylonautilus is an extinct genus in the nautiloid order Nautilida

Nautilida

The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species...

 from the Lower Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 of Europe and 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 Japan.

Tylonautilus has a coiled shell with a subquadrate whorl section, evolutely coiled with all whorls showing. The outer rim, the venter, has a smooth median depression bordered on either side by thread-like lirae, followed by rows of nodes, radially arranged. The suture has broad ventral and lateral lobes, 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...

is central.

Tylonautilus is a member of the Tainoceratidae which, with other related families, forms the nautilid superfamily Tainocerataceae. As with most if not all tainoceratids, Tylonautilus was probably a bottom dweller that spent its time crawling over or perhaps swimming close to the sea floor.