Mayfly Species Isonychia diversa (Slate Drakes)

A small brownish species, with pale wings and unique genitalia.

Head and thorax dark reddish brown, brightest on the notum; pleura somewhat paler. Fore femur dark red, becoming blackish at the apex. Tibia blackish. Tarsus pale reddish brown, the basal half of the first and second joints yellowish. Fore tarsus as long as the tibia. Middle and hind legs whitish; femora slightly tinged with reddish, claws pale smoky. Wings hyaline, venation wholly pale.

Abdomen smoky brown with a reddish brown tinge. Tergites 9 and 10 are dark red-brown, sternites 8-10 bright reddish. Middle sternites paler than tergites, somewhat translucent. Posterior margins of all segments conspicuously dark. Pleural fold pale at margin; above this pale line is a dark strip at the center, and a dark mark in the stigma. Mid-dorsal line pale, widened posteriorly. Dark brown submedian streaks margin it, and are in turn margined by paler translucent strips, and these by a darker line. Submedian streaks obscure basally, distinct apically. Postero-lateral angles dark brown; antero-lateral angles paler, translucent. Sternites marked as are the tergites, with a wider median line. Tails white, unmarked.

Forceps base reddish; deeply excavated on apical margin. Forceps pale. Penes reminiscent of Siphloplecton in their form. Wide and united at the base, they taper suddenly, but again curve outward to form more or less rounded apical lobes, separated by a V-shaped notch. Each has a slight indentation on the apical margin (see fig. 126). Second joint of forceps at least a third longer than the terminal joints combined. Basal joint rather long and slender.