Williamsoceras is an endocerid that Rousseau Flower (1968) added to his Allotrioceratidae (Flower 1955) on the basis of having a vertical partition within the siphuncle, known as a ventral process, with inter-connecting tubule-like structures along its margin where intercepted by endocones. Three species are named and described (Flower 1968) from the Garden City limestone of Whiterockian age near Logan and northern Utah, including the genotype Williamsoceras adnatum. Two other species come from the Juab limestone (Flower 1976) of near equivalent age in the southern Confusion Range in the Ibex area in western Utah.