Eusthenoceras
Eusthenoceras is a genus of Early Carboniferous nautiloid cephalopods with a large depressed, apically curved shell assigned to the Pseudactinoceratidae, (previously ranked as the subfamily Pseudactinoceratinae). The siphuncle is central or located between the center and venter. Necks are cyrtochoanitic, otherwise siphuncle shape and structure are unknown making inclusion in the Pseuactinoceratidae tentative. Siphuncle segments are probably inflated. "Eusthenoceras" is known only from the Lower Carboniferous of Ireland. Related "Bergoceras" is similar in overall form.