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Temporal range: Middle Ordovician - Middle Devonian
Scientific classification
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Nautiloidea
Order: Orthocerida
Family: Geisonoceratidae
Genus: Geisonoceras
Hyatt, 1884

Geisonoceras is an orthocerid genus named by Hyatt, 1884, and type for the Geisonoceratidae established by Zhuravleva in 1959. It has been found in North America, Europe, and Asia.

Shells are elongate, straight or slightly curved, and slowly expanding with a circular or subcircular cross section, trasverse aperture and slight hyponomic sinus. The surface has broad transverse bands with fine growth lines between. Sutures are straight, transverse or slightly oblique. The siphuncle is subcentral, necks short and straight, connecting rings slightly expanded into the chambers.


  • Walter A Sweet, 1964. Nautiloidea -Orthocerida, Treatise on Invertebrate Paleontology Part K, Endoceratoidea, Actinoceratoidea, Nautiloidea. Geological Society of America and Univ Kansas Press. Teichert and Moore (Eds)