Mayfly Species Rhithrogena futilis (Western Gordon Quills)

Scarcely distinguishable except on genital characters from Rhithrogena doddsi (now a synonym of Rhithrogena hageni). As compared with the type series of this latter species, the present one is slightly larger in size and the general color is a deeper brown. The abdomen is very narrowly ringed with light ochreous in the interspaceal area and on dorsum this pale area shows a faint smoky transverse streak. Anterior to the base of forewing is a light ochreous patch tinged with ruddy-brown posteriorly and bisected by a blackish streak. The usual dark streaks are present on the femora. As compared with those of doddsi the male genitalia show narrower and slightly more divergent penis-lobes apically, the centro-ventral small spine is lacking and in its place we find a small dorsal spine in much the same position; the minute apical spines on outer edge of each lobe which are present in most of the species of the group are somewhat better developed than in doddsi, but not as strong as in Rhithrogena morrisoni.