Dawsonoceratidae Flower, 1962

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 : 597

Family Dawsonoceratidae Flower, 1962 Genus Dawsonoceras Hyatt, 1884

Type species: Orthoceras annulatum Sowerby, 1818 , Wenlockian , Coalbrookdale, Shropshire, England .

Diagnosis.—Slender, circular or slightly compressed orthocones with symmetrically curved septa and straight transverse sutures. Sutures are parallel to annulation, positioned in groove of each annulation. Annulations are regularly spaced with fine transverse ornament or growth lines. Growth lines are in some species festooned. In some species, longitudinal ridges occur that may form nodes at ridges of annulations. Siphuncle is subcentral in early growth stages, central in late growth stages, narrow, but expanded within chambers. Septal necks are short suborthochoanitic to achoanitic, in advanced forms short reticulate. Incipient annulosiphuncular deposits and mural cameral deposits are known (after Kröger and Isakar 2006).