Mayfly Species Isonychia obscura (Slate Drakes)

A dark purplish brown species, with dark venation. Head and thorax dark purplish brown. Antenna dark purplish; purplish spots below the antennae. Purplish red spot at center of frontal margin. Lateral margins of pronotum and marks on pleura, somewhat paler. Lavender streak anterior to wing roots. Scutella black. Fore leg very dark purplish brown, tarsus slightly lighter than femur and tibia; base of femur light brown. Middle and hind legs white with greenish tinge; tarsal joinings narrowly purplish grey. Wings hyaline, venation dark purplish. Stigmatic area rather opaque white. Several stigmatic cross veins are forked.

Abdomen purplish brown, lighter in color ventrally. The anterior portion of each tergite is light brown, and a pale median dorsal streak extends the length of the abdomen. Posterior margins of all segments widely dark purplish brown. Dark submedian streaks margin the pale mid-dorsal area in the anterior portion of each tergite; from the dark posterior margin arise dark lateral streaks, rather diffuse. Pleural fold margined with purple. Ventrally, sternites 2-6 purplish rose, 7-9 a lighter shade of the same color. A wide cream margin parallels the pleural fold, and a narrow median pale line is bordered by wide purplish submedian streaks. A dark purplish brown streak, at its anterior end a dark dot, lies close to the pleural fold in the pale lateral area. Tails very dark purplish brown in the basal half, light grey distally; joinings reddish lavender. Forceps base dark reddish brown; forceps purplish brown. Forceps base very shallowly excavated apically; penes of the Isonychia arida type (see fig. 124).