''Hardmanoceras'' is a tarphycerid genus belonging to the

Trocholitidae The Trocholitidae are Tarphycerida with whorls in close contact as with the Tarphyceratidae, but in which the siphuncle, similar in structure, becomes dorsal. The Trocholitidae are derived from the Tarphyceratidae, perhaps from different tarphyc ...

from the upper

Lower Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. The ...

to possibly the lower Middle Ordovician, found in

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to th ...

. ''Hardmanoceras'' is like ''

Discoceras ''Discoceras'' is an extinct marine cephalopod mollusk, a member of the Trocholitidae in the Tarphycerida. It is distinct from '' Discosorus'', It is characterized by closely coiled, gradually expanding shells with a subquadrate cross section, ...

'' 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''.

References

* W.M Furnish and Brian H Glenister, 1964. Nautiloidea-Tarphycerida. Treatise on Invertebrate Paleontology, Part K, Mollusca 3. Teichert and Moore, eds. Geol Soc of America and Univ Kansas Press. Ordovician cephalopods of Oceania Prehistoric nautiloid genera Tarphycerida {{paleo-nautiloid-stub