Septum (marine biology): walls between each chamber, or siphuncle, in shells of nautiloids, ammonites, and belemnites; i.e. cephalopods that retain an external shell.
Winnipegoceras, named by Foerste (1922) for fossils found near Winnipeg in Manitoba, Canada, is known by it large, slender, compressed, strongly curved exogastric shells; long slender body chamber and siphuncle that is slightly removed from the venter which is the outer, longitudinally convex margin.