Jolietoceras is a compressed, annulate, lituiconic nautiloid included in the derived 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...

 family, Uranoceratidae

Uranoceratidae

Uranoceratidae is a family of Silurian barrandeoceroids that tend to become uncoiled with age and in which siphuncle segments tend to be expanded into the camerae.....

. The shell is gyroconic in the early stae, becoming straight and more rapidly expanded in the later. Sutures are straight and transverse. Surface annuli slope strongly to the rear, dorso-ventrally, in the early gyroconic stage but a lacking in the later straight segment.

Jolietoceras comes from the Middle Silurian of the United States (Illinois, Wisconsin).

The Uranoceratidae, including Jolietoceras, were one included in the Barrandeocerida (Sweet, 1964), which has since been incorporated into the Tarphycerida.