Mayfly Species Fallceon thermophilos

Abdominal tergites 2-6 of male imago dark olive brown, distinguished from all other known species by the very long third vein of the hind wing, which equals the other two veins in length.

Head and thorax shiny blackish. Legs smoky brown, with paler tarsi. Wings hyaline, venation pale. 7-8 stigmatic cross veins in the fore wing, without granulations. Hind wings long and narrow, and with three longitudinal veins; the third vein runs close to the hind margin, and equals the first two in length; between veins 2 and 3 is a single intercalary. The costal projection is rather blunt and short (see fig. 163).

Abdominal tergites 2-6 dark olive-brown, with pale narrow rings on the posterior margins. Tergites 7-10 opaque, brighter brown. Sternites pale ochreous. The bases of the forceps dusky, the two apical joints whitish; the last joint is narrow, and almost as long as the preceding one.