See text Eothinoceratidae is a family of Lower Ordovician nautiloid cephalopods included in the Cyrtocerinida.

The Eothinoceratidae as typified by Eothinoceras is characterized by slender slightly exogastric shells with a rather large siphuncle running along the convex ventral margin.

In addition to the type genus Eothinoceras the family is said to include Conothinoceras, Desioceras, Margaritoceras, Protothinoceras, Sacerdosoceras, and Saloceras summarized here.

[1] Desioceras Cecioni 1953 has a generally straight, narrow shell with a circular cross section covered with lirae.

[2] Margaritoceras Cecioni and Flower 1985 is found in the Obispo Formation, San Lucas, Bolivia.