Mayfly Species Rhithrogena anomala

A rather small reddish brown species; lateral spine-bearing projection on penes above base.

Head pale red-brown; clypeus pale hyaline; black semi-circular mark at base of antenna. Base of antenna pale; filament brown, tip pale. Thorax rather light red-brown, sometimes with yellowish tinge. Posterior and lateral margins of pronotum blackish. Tip of scutellum, lateral areas below it on each side, and small lateral patches anterior to it, purplish brown; two or three small yellowish patches anterior to scutellum. Blackish streak anterior to wing roots. Pleura paler than notum or sternum; large yellow areas near sternum anterior to middle and hind legs; narrow purplish black markings above bases of legs. Purplish intersegmental areas between prosternum and mesosternum. Fore leg light reddish brown, tarsus more yellowish, may be faintly smoky; apex of femur and tibia deeper red-brown. Middle and hind legs yellowish, tarsi faintly smoky; femora red-tinged. Small black spot (not streak) at center of each femur; small black dot at apex of each trochanter; short black streak above middle and hind coxae. Wings hyaline; longitudinal veins red-brown, cross veins colorless almost invisible; humeral cross veins dark red-brown. Stigmatic area opaque whitish.

Abdominal tergites 2-7 deep reddish brown with purplish tinge. Pleural fold and intersegmental areas pale hyaline; paler semi-hyaline elongate areas on each side near pleural fold. Mid-dorsal line narrowly pale hyaline; short wide submedian streaks at anterior margins, and two small pale spots, one on each side of median line, in posterior half of each tergite (on basal ones, these may connect with submedian streaks). Tergites 8-10 brighter red-brown, 10 distinctly reddish. Sternites hyaline; very similar in color to tergites, but paler; apical sternites paler than basal and middle ones. Genitalia reddish brown. Penes outcurved at tip; 2 or 3 serrations near inner apical margin of each side, and a short wide lateral process halfway from base to apex, at apex of which are several short spines (see fig. 101). Tails whitish, joinings distinctly red-brown. These are slightly larger than indicated for the type, but seem otherwise similar.

The species is allied to both Rhithrogena fasciata and Rhithrogena amica, from which it may be distinguished by the detailed structure of the penes and the redder coloration of body.