Ephippiorthoceras Foerste, 1924

Kröger, Björn, 2025, The Lyckholm acme of cephalopods - Review of the late Katian (Vormsi-Pirgu regional stages) Ordovician cephalopods of Estonia, European Journal of Taxonomy 978, pp. 1-169 : 34

Genus Ephippiorthoceras Foerste, 1924

Type species

Orthoceras formosum Billings, 1857 , from English Head, Anticosti Island, Quebec, Canada, English Head formation, zone 3 or 4 ( Foerste 1928c) (= Vauréal Formation, see Achab et al. 2011), late Katian; by original designation.

Diagnosis

Orthocones with circular to slightly compressed conch cross section; smooth or ornamented with fine transverse and /or longitudinal striae and lirae or coarse oblique plications; sutures form distinct broad lateral lobes; siphuncle subcentral to central, cyrtochoanitic septal necks; siphuncular segments expanded slendering adorally, parietal endosiphuncular deposits occur. (Compiled from Flower 1962, and Sweet 1964c.)

Remarks

Flower (1962: 33) assigned Ephippiorthoceras into his newly erected Proteoceratidae and justified it, without being more specific, among other arguments with the comment “other material indicates adoral slendering of the segments of the siphuncle.” Sweet (1964c: K256) assigned the genus with question into the Proteoceratidae and remarked that: “Details of the interior are not known in the type-species […] Ephippiorthocras is probably a pseudorthoceratid rather than a proteoceratid.” The material described herein suggests that Flower’s (1962) original evaluation was correct. In the Estonian specimens, a clear tendency for proteoceratid-like “slendering” is apparent. Moreover, the position of the siphuncle becomes more eccentric in later growth stages (see below).