The Tarphyceratidae are tightly coiled, evolute Tarphycerida with ventral siphuncles.

The siphuncle may be subcentral as in Centrotarphyceras; intermediary as in Tarphyceras, or subventral as in Campbelloceras.

Eurystomites is subquadrate and slightly compressed, with the maximum width closer to the dorsum.

Pionoceras is subrounded and slightly depressed with the maximum width closer to the venter.

The Tarphyceratidae are known mainly from the Lower Ordovician (M-U Canad); gave rise to the Trocholitidae and provided the sources for the more advanced barrandeocerids Genera in the Tarphyeratidae as named in the Treatise on Invertebrate Paleontology Part K (Furnish and Glenister 1964) are restricted to the middle and upper parts of the Lower Ordovician in North America.