Orthoceras brainerdi Whitfield, 1886, from Fort Cassin Formation, Floian, at Fort Cassin headland, Vermont; by original designation.
Slender, gradually expanding orthocones with broadly elliptically depressed cross section; short chambers; sutures directly transverse, slightly sinuous, forming gentle dorsal and ventral lobes; siphuncle large, almost marginal, circular cross section; connecting ring thick, concave segments; septal necks curved orthochoanitic to loxochoanitic; endosiphuncular deposits form endocones with narrow endosiphotube and three endosiphoblades (after Flower 1941; Ulrich et al. 1944: 55; Teichert 1964: K166).
Numerous species have been assigned to Proterocameroceras, especially from the Early and Middle Ordovician of Russia (Balashov 1962, 1968) and South China (Xu & Lai 1987); some of them differ strongly from the type species. Proterocameroceras valhallfonnense sp. nov. (see below) is one of these forms. A revision of this genus is therefore desirable, but not within the scope of this monograph.