Protocycloceras Hyatt, 1900

Kröger, Björn & Pohle, Alexander, 2021, Early-Middle Ordovician cephalopods from Ny Friesland, Spitsbergen - a pelagic fauna with Laurentian affinities, European Journal of Taxonomy 783 (1), pp. 1-102 : 52-53

Genus Protocycloceras Hyatt, 1900

Type species

Orthoceras lamarcki Billings, 1859 , from the Fort Cassin Formation (Floian Stage), Township of Godmanchester, Huntingdon County, southwest Quebec; by original designation.

Diagnosis

Nearly straight, annulated longicones with circular or subcircular cross section and straight sutures; camerae narrow, about 6–7 over a length similar to conch cross section; siphuncle located between center and ventral conch margin; siphuncular segments concave; septal necks short, loxochoanitic to orthochoanitic; connecting ring comparatively thick; siphuncular deposits wedge out adorally at steep angle to ventral side; diaphragms in apical portions of siphuncle; epi-and hyposeptal cameral deposits more strongly developed on ventral side (adopted from Kröger & Landing 2009).

Remarks

The genus Protocycloceras is type genus for the Protocycloceratidae Kobayashi, 1935 . Based on the cladistic analysis (below) this family is abandoned. The genus clusters consistently with other members of the Troedsonellida, such as Buttsoceras (see below). The close relationship between the two genera is also suggested by the combination of diaphragms and endosiphuncular linings, which is unknown in any other genus.