''Landeroceras'' is a genus of straight shelled cyrtogomphoceratid from the Middle Ordovician Big Horn dolomite of Wyoming. The shell of ''Landeroceras'' is a subcylindrical brevicone with the

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

on one side, determined as ventral. Siphuncle segments are short and well expanded into the chambers. Connecting rings are thick, septal necks cyrochoanitic to recumbent, bullettes markedly swollen. ''Landeroceras'' is at the end of a small offshoot within the discosorid family Cyrtogomphoceratidae that also includes ''

Cyrtogomphoceras ''Cyrtogomphoceras'' is a genus of nautiloid cephalopods, recognized by its large breviconic shell with a notable endogastric curvature. The shell is fusiform in profile, reaching maximum width at or near the base of body chamber, which narrows t ...

'', and not in the line which gave rise to the

Phragmoceratidae The Phragmoceratidae is a family of extinct nautiloid cephalopods from the Order Discosorida that lived during the latter part of the Silurian. Diagnosis Phragmoceratids are characterized by generally compressed, upwardly curved endogastric sh ...

References

* Flower, R H and Teichert, C., 1957. The Cephalopod Order Discosorida. University of Kansas Paleontological Contributions. Mollusca, Article 6, pp 1–144. * Teichert C. 1964. Nautiloidea -Discosorida, Treatise on Invertebrate Paleontology, Part K. Teichert and Moore eds. Discosorida Middle Ordovician first appearances Late Ordovician extinctions Prehistoric nautiloid genera Natural history of Wyoming {{ordovician-animal-stub