Wikipedia
Bathmoceras
Bathmoceras is a primitive cephalopod genus from the Middle and Upper Ordovician, type for the family Bathmoceratidae, order Ellesmerocerida.
Furnish and Glenister, 1964 include Eothinceras in the Bathmoceratidae along with Bathmoceras. Flower, 1964, separates the two genera into their respective families which he included in his suborder, Cyrtoceritina