Mayfly Species Cinygma dimicki (Western Light Cahills)

Head pale yellowish faintly tinged with light brownish on vertex. Pronotum pale ochreous tinged with brownish, each lobe bordered laterally by a black line and with an oblique black median streak; a strong black streak at base of foreleg. Mesonotum pale brownish, lateral edges and scutellum light yellow; pleura pale brownish with a light yellow patch anterior to wing base, this patch bordered both dorsally and ventrally by distinct black streaks; black streaks at bases of both mid and hind legs. Metanotum pale brownish with a paler, more yellowish, median projection. Abdomen with segments I-VII pale hyaline yellowish, each segment with narrow posterior black border and with dark streak on posterior half of lateral edge; last three segments opaque, tinged with light brown. On all but the first and the last two segments there are indistinct, lateral, L-shaped smoky marks with small commalike streaks attached ventrad to the anterior ends of same. Ventrally pale yellowish, the two posterior segments faintly tinged with brownish. Forceps pale smoky; setae deep smoky with fine dark intersegmental rings. Legs dull amber, the tibiae and tarsi tinged with smoky, the femora twice-banded with purple-brown, coxae with a black streak. Wings hyaline with fine dark veins and crossveins.

The male genitalia are quite similar to those of Cinygma integrum, but the stimuli are smaller, and the apex of each lobe of the penes is evenly rounded and without the slight tooth found in integrum, there is also less of a lateral excavation at the junction between the basal and apical sections. Both species show a pair of minute spines dorsally near the base of cach lobe of penes, a feature not shown McDunnough's drawing of Cinygma integrum (1926, Can. Ent. LVIII, 302).