Hardmanoceras is a Tarphycerid

Tarphycerida

The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician to the Middle Devonian. Some like Aphetoceras and Estonioceras are loosely coiled, gyroconic, others like Campbelloceras, Tarphyceras, and Trocholites are tightly coiled, but...

 genus belonging to the Trochilidae from the upper Lower Ordovician to possibly the lower Middle Ordovician, found in Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

. Hardmanoceras is like Discoceras

Discoceras

Discoceras, a member of the Trocholitidae in the Tarphycerida, not to be confused with Discosorus.Discoceras is characterized by closely coiled, gradually expanding shells with a subquadrate cross section, that may be ribbed or smooth. The sides are broadly rounded; the venter wide and slightly...

but prominently ribbed and with a depressed whorl section. The body, or living, chamber is long, 1 1/8 volutions long. The ultimate portion is slightly divergent, not an uncommon characteristic of tarphycerids.

Harmanoceras was named by Teichert and Glenister in 1952. The type us Hardmanoceras lobatum.