Cyrtogomphoceratidae Flower, 1940

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 : 604

Family Cyrtogomphoceratidae Flower, 1940 Genus Strandoceras Flower, 1946

Type species: Protophragmoceras tyriense Strand, 1934 , Gastropod Limestone , Ashgillian , Late Ordovician , Stavnestangen, Ringerike, Norway .

Diagnosis.— Strandoceras is unique within Cyrtogomphoceratidae with regard to its general shell shape. Strandoceras is strongly compressed cyrtocone with narrowly rounded venter that is circumvented by shallow longitudinal furrow at left and right flank in direct vicinity of siphuncle. In commonality with other Cyrtogomphoceratidae , Strandoceras has siphuncle at concave margin of conch, sutures with shallow lateral lobe and acute ventral saddle, septal necks are short cyrtochoanitic. Siphuncular tube is thick, strongly expanded within chambers. Aperture is open with shallow peristomal saddle at flank. Protophragmoceras Hyatt in Zittel, 1900 differs in more symmetric siphuncular shape and non−marginal siphuncular position. Moreover, Protophragmoceras is less compressed and displays peristome with sharp hyponome at venter (after Flower, 1946).

Remarks.—The genus was assigned to the Cyrtogomphoceratidae by Teichert (1964). However, Dzik (1984) regarded the genus as a subjective junior synonym of Protophragmoceras Hyatt in Zittel, 1900 of the Phragmoceratidae . The idea of Dzik (1984) can not be followed here because Strandoceras clearly differs in several aspects from Protophragmoceras (see genus diagnosis).

Occurrences.—Middle to Late Ordovician, Baltoscandia and Wales.

Included species.— Codoceras schmidti Teichert, 1930 , Cyrtoceras sonax Salter, 1866 , Phragmoceras sphynx Schmidt, 1858 , Strandoceras strandi Sweet, 1958 , Protophragmoceras tyriense Strand, 1934 .