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.
Williamsoceras is characterized by a ventral process within the siphuncle that extends vertically from the bottom side, essentially bisecting the interior.
and is slightly sinuous in profile (Flower 1968, 1976) Williamsoceras is similar to Cacheoceras which comes from the same areas and formations, except that Cacheoceras has additional smaller processes, either one on the dorsal side opposite the main process or a pair that are positioned dorsolaterally.
Williamsoceras may have its origin in the Manchuroceratidae from the upper Canadian of northern China and Korea (Flower 1955, 1968, Teichert 1964) derived from the Proterocameroceratidae, by a lengthening of the septal necks.