Mayfly Species Stenacron pallidum (Light Cahills)

A small pale species of Stenacron interpunctatum group; black markings on face and pronotum; basal joint of fore tarsus slightly less than half of second; no dark spiracular dots; faint median band on hind femur.

Head pale yellowish; a small reddish spot at center of vertex; black dash below each antenna; base of antennal filament dusky, tip pale. Thoracic notum yellow to yellowish brown; pleura slightly deeper yellow. A black longitudinal streak on each side of pronotum, no other dark markings. Sternum yellowish, with deeper orange area at each side near base of hind leg. Legs yellowish white; fore femur yellowish brown, with conspicuous median and apical purplish black bands. Similar but paler dark bands on other femora. Fore tibia purplish black at apex; tarsal joinings of fore leg, claws, and tips of distal tarsal joints of other legs, faintly brownish. Basal joint of fore tarsus half the length of the second. Wings hyaline; markings as in S. interpunctatum; fourth apical intercalary narrowly darker than others; 4 to 5 basal costal cross veins, 2 oblique ones at bulla, about 12 beyond. Cross veins in anal region of wing rather pale.

Abdominal segments 1-7 hyaline or semi-hyaline, whitish. Rather wide purplish black posterior margins on tergites; no dark spiracular dots. Segments 8-10 opaque, tergites faintly yellowish, sternites whitish. Genitalia very similar to those of S. interpunctatum. Tails pale, not darker at joinings.

This species is very similar to interpunctatum, and may in fact prove to be synonymous with it. For the present we hold it to be a distinct species, because of the faint but distinct dark median band on hind femur, the longer basal joint of the fore tarsus, and the paler thoracic notum and apical abdominal tergites. The basal joint of the fore tarsus, while not as long relatively as in heterotarsale (now a synonym of S. interpunctatum), is yet rather intermediate in length between that species and interpunctatum