The figure below shows the distribution of samples containing the nautiloid cephalopod Geisonoceras.

[ Geisonoceras distributin ]

Geisonoceras is a common nautiloid in the MRV strata.

[ Geisonoceras ]

Geisonoceras Haytt, 1884 [*Orthoceras rivulae ]
Slowly enlarging orthocones or cyrtocones of circular to subcircular cross section and with straight transverse or slightly oblique sutures. Siphuncle subcentral; necks short or straight, connecting rings expanding slightly within camerae. Small adorally attenuated annulosiphonate deposits in adapical siphuncular segments; camarae with episeptal and hyposeptal deposits. Surface with broad transverse bands, between which are fine growth lines. Aperture transverse, with slight hyponomic sinus.
M. Ord. - M. Dev., North America, Europe, Asia
Family Geisonoceratidae Zhuravleva, 1959
Orthoconic or cyrtoconic conchs of subcircular cross section, with orthochoanitic to suborthochoanitic siphuncle occupied by endosiphuncular annuli restricted to septal foramen or growing anteriorly against connecting rings; in advanced species, endosiphuncular annuli fusing with those of adjacent segments to form continuous siphuncular lining.
M. Ord. - M. Dev.
Order Orthocerida Kuhn, 1940

Treatise on Invertebrate Paleontology, K236.