Mayfly Species Rhithrogena morrisoni (Western March Browns)

A species of the Rhithrogena brunnea (now a synonym of Rhithrogena hageni) group; humeral cross vein blackish; penes outcurved at tip.

Head and thorax dark brown. Pleura largely dark, but with several yellow spots. Fore legs brown; tips of tibiae darker. Middle and hind legs paler, femora with dark brown streaks. Wings hyaline; venation fine, brown. Humeral cross vein deep blackish. Stigmatic area tinted with smoky; cross veins mostly anastomosed or forking. Abdominal tergites dull brown, apical ones darker; posterior margins darker, lateral margins pale yellowish. Sternites dull yellowish, immaculate. Forceps dark brown. Tails dull yellowish to brownish, joinings not noticeably darker. Penes strongly divergent apically, narrowed toward the tip; a small but distinct ventral spine on each lobe, and 5 to 6 small spines ventrally near apex (see fig. 100, after McDunnough). Basal joint of forceps slightly swollen on inner margin.

Allied to Rhithrogena brunnea (now a synonym of Rhithrogena hageni), but with weaker mid-ventral spine on the penes, and stronger apical spines.

Described as R. petulans

Body length 10 mm, wing length 11 mm

A species closely allied to R. brunnea (now a synonym of Rhithrogena hageni); penes narrowed at apex, a small median ventral spine on each.

Frontal portion of head deep smoky grey; red-brown shading at bases of ocelli; vertex dark red-brown. Greyish streak across face in antennal region; antennae dark red-brown, tips paler. Pronotum dark olive-brown; darker brown shading along posterior margin. Mesonotum light red-brown with an olive tinge; median streak darker than area on each side. Pale spot anterior to scutellum; dark area on each side of this, from which a dark line extends forward above wing roots. Scutellum and all posterior portions of mesonotum, and posterior half of metanotum, blackish brown. Purplish streak anterior to wing roots. Intersegmental areas of pleura paler, yellowish brown. Narrow dark lines above leg bases. Sternum dark red-brown; anterior portion of mesosternum rather paler. Fore legs dark red-brown; middle and hind legs yellowish olive to yellow-brown. Black longitudinal streak, tapered at each end, on basal half of each femur. Coxae olive brown. Black spot at apex of each trochanter; apices of middle and hind femora, and tarsal joinings of these legs, deep brown; tarsi smoky brown. Wings hyaline; stigmatic area distinctly brown-tinged. Venation dark red-brown; longitudinal veins, especially in anterior half of fore wing, somewhat heavier than cross veins. Humeral cross vein deep purple-black. Basal costal cross veins well defined; about 6 before bulla, those in stigmatic area anastomosed as usual. Slight tendency for cross veins in 3rd and 4th spaces below bulla to be somewhat closer together than usual.

Abdominal segments 2-7 semi-hyaline, light purplish brown with reddish tinge; tergites darker than sternites. Intersegmental areas and lateral margins narrowly paler; posterior margins of tergites narrowly darker dorsally. Traces of a narrow pale mid-dorsal line, short submedian dashes near center of each tergite, and lateral faintly defined wedge-shaped areas based on anterior margin. Segments 8-10 opaque, brighter red-brown, with distinct yellowish tinge. Basal portion of forceps base pale; forceps deep brown, penes paler. Penes only slightly outcurved at apex; small apical spines rather well developed; small ventral spine near middle of each lobe; penes narrowed toward apex. (See fig. 100). Tails deep smoky brown; basal joinings darker, others somewhat opaque.