Mayfly Species Heptagenia dolosa

A pale species closely allied to Heptagenia marginalis; genitalia of the Heptagenia flavescens type.

Head pale yellowish white; frontal shelf hyaline, anterior margin narrowly purplish black; a faint line of same color on each side of carina below antenna. Base of antenna white; filament faintly dusky at base, tip pale. Four small inconspicuous spots on vertex; two on posterior margin, two anterior to these, one near each ocellus. Eyes very large, blue-black in alcohol. Thorax pale yellowish white. Lateral margin and an oblique lateral stripe on pronotum black; a black streak above fore coxa. Two large and one small black spots above middle coxa, arranged as in H. marginalis; a small black dot above and behind hind coxa, similar dark dot on lateral margin of metanotum. Mesonotum unmarked. Legs pale whitish; extreme base of fore femur reddish brown; a narrow apical streak, a wide median band, and a streak along the ventral edge, deep purplish red. Apex of fore tibia, and distal tarsal joint, narrowly brown; basal tarsal joint with faint brown shading. Middle and hind femora pale basally, median bands pale and incomplete; apical streak often incomplete, apices of tibiae and tarsal claws purplish. Three main veins of costal margin heavy, yellowish; other veins fine, brownish: 4 to 5 costal crossveins before bulla, 12 to 15 beyond it.

Abdominal segments 1-8 white, hyaline; 9 and 10 opaque, creamy yellow. Posterior margin of each tergite narrowly purplish black; a blackish longitudinal streak on each side of each tergite, halfway between median line and pleural fold; a faint oblique dark mark at each spiracle; tergites 6 and 7, occasionally also 9 and 10, with traces of a faint dark mid-dorsal streak. Dark markings less prominent than in H. marginalis. Genitalia creamy white. Details of structure of penes differ somewhat from marginalis (see fig. 95). Second forceps joint somewhat shorter relatively than in that species. Tails wholly whitish.

The smaller size, paler color of tail, single median femoral band, lack of dark mesonotal markings and more restricted mid-dorsal markings on tergites, as well as details in the structure of the penes, distinguish this species from marginalis.