Orthocone / Orthoceras

The shell of Orthoceras is shaped like a slowly tapering cylindrical cone, and is made up of closely spaced concavo-convex chambers, joined together by a centrally placed tube called a siphuncle (the tube connecting the chambers of the shell).
Orthoceras was an active swimmer, with the shell positioned horizontally in the water. It scavenged and predated on small animals.