Ordogeisonoceras Frey, 1995

Kröger, Björn, 2013, The cephalopods of the Boda Limestone, Late Ordovician, of Dalarna, Sweden, European Journal of Taxonomy 41, pp. 1-110 : 46-48

Genus Ordogeisonoceras Frey, 1995

Type species

Orthoceras amplicameratum Hall, 1847 from the Trenton Formation, latest Katian, Middleville, New York, USA.

Diagnosis

Slender, gradually expanding orthocones; ornamented with fine longitudinal lirae; circular in cross section with straight, transverse sutures; chamber distance ca. one-half of the corresponding conch diameter; siphuncle eccentric; siphuncular segments subtubular, slightly expanded within chambers; siphuncular diameter 0.14–0.2 of corresponding conch cross section; septal necks moderately long, suborthochoanitic; endosiphuncular deposits consisting of small annuli, restricted to the apical portions of the phragmocone; cameral deposits well developed. (Adopted from Frey 1995.)

Remarks

In the original diagnosis, the septal necks were described as “orthochoanitic”, but this is imprecise; the figures of the type species in Frey (1995: pl. 3, figs 4, 5, 8) indicate suborthochoanitic septal necks.