Pomerantsoceras, Kröger, 2007

Kröger, Björn, 2007, Concentrations of juvenile and small adult cephalopods in the Hirnantian cherts (Late Ordovician) of Porkuni, Estonia, Acta Palaeontologica Polonica 52 (3), pp. 591-608 : 602

Genus Pomerantsoceras nov.

Derivation of the name: In honour of Marko Pomerants who is an activist in protection and restoration of natural and historical monuments of the scenic Porkuni, Estonia.

Type species: Pomerantsoceras tibia sp. nov., monotypic.

Diagnosis.— Pomerantsoceras differs from other Graciloceratidae mainly in having slowly enlarging, only sightly cyrtoconic conch which resembles orthoceratidans. Cross section is compressed with ratio conch width/height 0.8. Septal spacing is narrow with approximately 0.2–0.25 of conch height. Septal curvature is very shallow. Sutures have shallow lateral lobe. Septal necks are achoanitic. Siphuncle is marginal, positioned at convex side of conch curvature, and very thin tubular with cross section less than 0.10 of conch. Apex is spherical and cap−shaped, without constriction, with cicatrix. No endosiphuncular deposits are known. Adult conch length is approximately 20 mm.

Remarks.—The enigmatic Michelinoceras ? ivorense Flower, 1946 from the Late Ordovician of Indiana, USA resembles Pomerantsoceras with respect to the shape of the conch and septal spacing, but its internal characters are not known. Stratigraphic and geographic range.—Siuge Member, Porkuni Regional Stage, Late Ordovician from Porkuni, north Estonia.