What is "adnatoceras"

Adnatoceras is a mid Devonian to Pennsylvanian orthoconic nautiloid cephalopod included in the pseudorthocerid family Spyroceratidae, characterized by tubular, straight-sided, siphuncle segments that expand abruptly at the septal foremena. In some species the siphuncle segments become more ovoid in the later grow stages. The name Adnatoceas comes from the wide area of contact, or adnation, between the connecting ring and flared out brim of the cyrtochaoanitic septal neck.