Mayfly Species Ameletus cooki (Brown Duns)

A small clear-winged species. Head blackish. Prothorax and postero-lateral portions of the mesothorax and metathorax also blackish. Mesothorax brown dorsally, with orange shading before the wing root and on and before the scutellum. Pleura and sternum largely blackish, shaded with orange at the bases of the legs, most prominent around the middle legs.

Fore legs blackish brown; middle and hind legs lighter brown, the basal joints tinged with orange-brown. Wings hyaline; longitudinal veins light amber, the cross veins pale and indistinct, except in the stigmatic area, where they are smoky.

Dorsum of abdomen orange-brown. Suffused brown shading along the lateral margin, tending to form obscure semi-triangular patches in the postero-lateral corners; sometimes extending narrowly along the posterior margin. Trachea of the anterior segments forming a black network. Sternites 2-6 dull hyaline whitish, with traces of orange on the ganglionic areas. Sternites 7 and 8 opaque, bright yellowish; sternite 9 largely blackish brown shaded with orange. Forceps base yellowish. Penes long and rather slender, each bearing a spine on the inner margin near the middle; penes curved only at tip (see fig. 116). Tails dirty whitish, the joinings dark.