. Bulletin. Natural history; Natural history. 76 Natural History Survey Bulletin \'<)1. 26, Art. 1 The winns of some adults arc washed with red or oranjje, but those of most are hyaline. In the fore win}:, there are quite numerous, weak crossveins, fijz. .^0, numer- ous, short marginal intercalaries, and the outer winn margin is always slightly scal- loped. The median intercalary vein and Mo extend almost to the wing base. There are no cubital intercalaries. Vein lA extends to the outer wing margin, and a series of irregular, weak intercalary veins extends from lA to the anal win
. Bulletin. Natural history; Natural history. 76 Natural History Survey Bulletin \'<)1. 26, Art. 1 The winns of some adults arc washed with red or oranjje, but those of most are hyaline. In the fore win}:, there are quite numerous, weak crossveins, fijz. .^0, numer- ous, short marginal intercalaries, and the outer winn margin is always slightly scal- loped. The median intercalary vein and Mo extend almost to the wing base. There are no cubital intercalaries. Vein lA extends to the outer wing margin, and a series of irregular, weak intercalary veins extends from lA to the anal wing margin. The hind wing is almost circular in outline, fig. 176, has a broad costal projection near the wing base, and numerous weak crossveins and numerous marginal intercalaries; vein M is forked near the center of the wing. The abdomen is stocky in the basal half, but the segments are markedly more slender and elongate from the sixth segment pos- teriorly. The male genitalia, fig. 174, very similar throughout the genus, are composed of a pair of three-segmented forceps and a pair of subcortical penis lobes which are fused on the median line almost to the tips. The apical margin of the terminal abdominal segment in the females has a pair of sub- median, triangular projections with a V- shaped notch on the meson between them. The median caudal filament is vestigial in both the male and female adults. In the subimagoes, the wings are heavily shaded with dark brown or black; white spots surround the crossveins and often two vague, white bands extend obliquely across each wing. The nymphs, the first one of which was described by Walsh (1864), are among the most unique and distinct of all mayfly naiads, fig. 181. In these nymphs, the integument is more heavily armored than in any other Nearctic species. The head is small and hypognathous; a pair of small frontal horns is usually present between the bases of the antennae; and the genae are produced above the bases of the mandibles
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