The 25 species of the genus Ephemerella Walsh in North America formerly placed in the subgenera Ephemerella, s. s. (=invaria-group auct.), and Chitonophora (Bengtsson) (=needhami-group auct.) are placed in the subgenus Ephemerella, s. s. Characters do not allow grouping of the nymphs and adults in concordant groups that correspond with the 2 subgenera previously recognized. Accounts are given for the nymph and male adult of each species including synonymies, synoptic descriptions, and distribution records and maps. Illustrated keys are given for the nymphs and male adults. E. euterpe Traver is regarded as a synonym of E. maculata Traver. E. lacustris is described from imagoes and nymphs from Wyoming, and E. verruca from Oregon, E. simila from West Virginia, E. rossi from Tennessee, and E. crenula and E. hispida from North Carolina and Tennessee are described from the nymphal stage only.