1. Penes with long apical lobes and a deep median notch; penes without spines or with only dorsal median spines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ephemerella needhamiPenes with short apical lobes and a shallow median notch; penes almost always withdorsal and/or ventral lateral spines. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Second segment of genital foreceps without a distinct meso-apical lobe. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ephemerella excrucians
Second segment of genital forecepts expanded inot a distinct meso-apical lobe. . . . . . . . . . . 3
3. Penis lobes short and broad with nearly parallel lateral margins; dorsal aand ventral spines present; thorax and abdomen pale yellow. . . . . . . . . . . . . . . . . . . . Ephemerella dorothea
Penis lobes not so short and broad, usually with round lateral margins; dorsal and ventral sines not arranged as precededing; thorax and abdomen brown or reddish brown, if yelow always shaded with brown or tan. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
4. Posterior margin of subgenital plate with a distinct median projection; penes with 6-8 median basal spines on dorsal surface and with 1-4 apical or subapical spines . . . . . . . . . . . . . . . . 5Posterior margin of subgenital plate gently rounded; penes with only 1 or 2 and no basal spines on the dorsal surface, and without or with only 1 or 2 apical spines. . . . . . . . . . . . . . 6
5. Penes with long spines; penes usually with more than 15 dorsal spines and with paired ventral subapical spines; abdominal terga yellow with a brown transverse band. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ephemerella rotunda
Penes with short spines; penes usually with less athan 12 dorsal spines and with paired ventral apical spines; abdominal terga reddish brown. . . . . . . . . . . . . . . . . . . Ephemerella invaria
6. Penes usualy with 12 or more dorsal spines and without ventral spines; forewirng with light brown to reddish-brown pirmary longitudinal veins. . . . . . . . . . . . . Ephemerella subvaria
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Key to the Species of Ohio Adult Ephemerella