The relationships and taxonomy of the known North American species of the subgenus are discussed. Of the 23 specific names heretofore recognized, the number is reduced to 15 valid species by new synonymies and the reduction of two to subspecific rank. Ephemerella grandis Eaton is polytypic, with subspecies E. g. grandis Eaton, new status (=glacialis carsona Day, new synonymy), E. g. ingens McDunnough, new status (=glacialis Traver, proserpina Traver, new synonymies), and E. g. flavitincta McDunnough, new status. Additional new synonymies are as follows: Ephemerella cornuta Morgan (=depressa Ide), E. tuberculata Morgan (=cherokee Traver), E. flavilinea McDunnough (=lapidula McDunnough), E. coloradensis Dodds (=wilsoni Mayo) and E. spinifera Needham (=autumnalis McDunnough, sierra Mayo). Geographical or age variation, or both, are described, especially for the nymphs, of most species of the subgenus. Illustrated keys are given to the nymphs, and to the adults as far as known; and complete synonymies and distributions are included.