Permonautilus is an extinct nautilid

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 Upper 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 Russia, Named and described by Kruglov in 1933. Permonautilus is an involute, globular, spinose member of the Lirocertidae which are included in the Clydonautilaceae

Clydonautilaceae

The Clydonautilaceae is a superfamily within the nautiloid order Nautilida characterized by smooth, generally globular, shells with nearly straight sutures, in early forms but developing highly differentiated sutures in some later forms...

. Whorl sections are broad, with a rounded venter. The umbilicus in the middle of the shell is deep, from which spine-like processes extend laterally in the mature portion near the aperture. 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...

 in Permonautilus is subcentral, the suture, slightly sinuous.

Externally, Permonautilus closely resembles the Pennsylvanian

Pennsylvanian

The Pennsylvanian is, in the ICS geologic timescale, the younger of two subperiods of the Carboniferous Period. It lasted from roughly . As with most other geochronologic units, the rock beds that define the Pennsylvanian are well identified, but the exact date of the start and end are uncertain...

 - Lower Permian Solenochilus

Solenochilus

Solenochilus, type genus of the Solenochildae is an extinct cosmopotilian nautilid from the Lower Pennsylvanian to the Lower Permian with a rapidly expanding, coiled globular shell with few whorls, from which prominent spines extend laterally from the umbilical area at maturity...

and the Upper Mississippian Acanthonautilus

Acanthonautilus

Acanthonautilus is an extinct genus in the nautilid family Solenochildae from the Upper Mississippian of North America and equivalent strata in Europe, first described by Foord in 1896....

, both which belong to the Aipocerataceae

Aipocerataceae

The Aipocerataceae is a superfamily within the Order Nautilida characterized by rapidly expanding, smooth to ribbed, cyrtoconic to coiled shells with rounded or sometimes dorsally flattened or impressed whorls, nearly straight sutures, and a ventral and marginal siphuncle. Septal necks are...

; except for the subcentral siphuncle.