Mayfly Species Eurylophella prudentalis (Chocolate Duns)

A member of the bicolor group (now a synonym of Eurylophella bicolor), related to E. temporalis (now a synonym of Eurylophella temporalis). There is a globular swelling on the penes halfway from base to apex.

Eyes orange. Head yellowish brown; a curved black streak beneath each antenna. Thorax reddish brown, the pleura and the anterior portion of the mesonotum yellowish; several black dots on the pronotum. Metasternum purplish red. Fore leg amber yellow, a brown spot at the apex of the tibia. Middle and hind legs paler yellow; claws and tarsal joinings narrowly reddish brown. Wings hyaline; venation hyaline. On each main vein of the fore wing, and on median vein of the hind wing, is a short brown basal streak; on each wing also, a faint basal brownish stain. Abdominal tergites reddish brown, shading into yellowish apically. Posterior margin of the basal and middle tergites, and the pleural fold, blackish brown. Short dark submedian streaks or dots on the anterior margin of each tergite. Black stigmatic dashes. Ventrally paler, the basal sternites faintly washed with yellowish brown. Black dots and dashes distinct. Tails yellowish white, joinings purplish black.

Occipital tubercles are present in nymphs of both sexes, but are only moderately developed. The rows of dorsal spines are widest apart on the basal tergites, and converge to rearward. The spines on tergites 1-3 are finger-like and taper bluntly, but are shorter and less curved than in E. temporalis (now a synonym of Eurylophella temporalis). Postero-lateral spines on segments 2 and 3 are only moderately developed. In color the nymph resembles a dark temporalis; in some specimens a pale dorsal stripe is present. The hinge of the operculum is pale, and the operculum itself is sprinkled with pale dots. Tails not noticeably banded, but each joining is darker.