Mayfly Species Epeorus longimanus (Slate Brown Duns)

A rather pale brownish species; genitalia of the longimanus type (now a synonym of Epeorus longimanus). (see fig. 105).

Head light reddish brown. Thoracic notum light yellowish to reddish brown ochre, pleura and sternum very similar in color. Fore femur and tibia “translucent raw umber” (Eaton); other femora similar, tibiae yellowish brown. All femora with a round black spot near the middle; fore tibia blackish at apex. Fore tarsus dull yellowish brown, middle and hind tarsi slightly paler in color; tarsal joinings may appear somewhat darker. Wings hyaline; venation light brownish amber, the humeral cross vein, base of subcosta and other longitudinal veins behind it, paler; veins in hind wing rather pale.

Abdominal tergites 2-9 “tinged extensively with light brownish” (Eaton); 9 and 10 often light brown-ochre. Tergites 2-7 semi-hyaline; posterior margins deep purplish brown, this band not extending around the postero-lateral angle, but a short dark oblique streak arising from this dark band runs to the spiracular area. Purplish brown shading along mid-dorsal line; median line narrowly pale, with darker streak on each side. Pale lunate submedian marks on each side lie within the shaded area. Segments 8-10 opaque. Sternites pale yellowish; nerve cord and ganglia whitish, opaque; sometimes traces of pale submedian oblique streaks on basal and middle segments. Tails “light warm sepia brown” (Eaton). Apical margin of forceps base projects backward as a dome-shaped structure, concealing the bases of the penes. Each division of the penes has an erect apical lobe and a larger laterally-directed one, bearing a sharp lateral spine. A median pair of strong spines is present, their tips divergent.

In type of genitalia this western species is allied to the eastern I. fraudator (now a synonym of Epeorus pleuralis), I. fragilis (now a synonym of Epeorus fragilis) and I. tenuis (now a synonym of Epeorus fragilis). It is larger and somewhat darker in color than either of the two latter species. The lobes of the penes are likewise much less deeply cut than in any of the three. The darkest specimens we have seen are slightly paler than typical fraudator, which is likewise a little larger than I. longimanus.

Described as I. proprius

Body length 9-10 mm, wing length 10 mm

Similar in general appearance to I. longimanus (now a synonym of Epeorus longimanus), but with genitalia of the pleuralis (now a synonym of Epeorus pleuralis) type.

The only specimens available are so faded from long immersion in alcohol that it is impossible to be certain of the original color. However, they seem to have been very similar to I. longimanus, from which species they are distinguishable mainly by the very different type of genitalia. A comparison of these with specimens of longimanus which likewise have been in alcohol for several years, shows that the dark spot on each femur is smaller and less distinct than in the latter species. The oblique black streak present on the postero-lateral angles of the tergites in I. longimanus, is apparently lacking in I. proprius (now a synonym of Epeorus longimanus). Genitalia very similar to I. pleuralis, but smaller; chitinized appendage attached to dorsal lobe of penes is narrower and more distinctly sickle-shaped than in that species. (See fig. 106).