''Leurorthoceras'' is a genus of flattened actinoceratids with a

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

narrower than in ''

Actinoceras ''Actinoceras'' is the principal and root genus of the Actinoceratidae, a major family in the Actinocerida, that lived during the Middle and Late Ordovician. It is an extinct genus of nautiloid cephalopod that thrived in the warm waters of the Un ...

'', segments of which tend to become longer in the mature parts of the phragmocone, the chambered part of the shell. This fossil is known from the Middle Ordovician of North America, Europe, and Siberia.Curt Teichert, 1964. Actinoceratoidea, Treatise on Invertebrate Paleontology, Part K. Geological Society of America and University of Kansas Press.

References

Prehistoric nautiloid genera Paleozoic life of Nunavut Ordovician cephalopods of North America Ordovician cephalopods of Europe {{paleo-nautiloidea-stub