40 ILLinoris NarurAL History Survey BULLETIN 
ae iar ae 
Fig. 68.—Hexagenia bilineata, dorsal aspect 
of head of nymph. 
Fit. 69.—Hexagenia limbata, dorsal aspect 
of head of nymph. 
Fig. 70.—Hexagenia atrocaudata, dorsal as- 
pect of head of nymph. 
Fig. 71.—Hexagenia munda, dorsal aspect 
of head of nymph. 
rower than diameter of one eye. Thorax 
typically mostly dark red-brown, varying 
to light brown; fore wing hyaline or faintly 
stained with yellow or tan, costal interspace 
shaded with red-brown, usually several 
prominent, brown spots in disc of wing; 
outer margin of hind wing usually with a 
conspicuous brown band. Abdominal ter- 
gites typically marked with dark brown 
lateral triangles and lighter brown mesal 
ones, sternites varying from almost com- 
pletely unmarked to having a conspicuous 
row of dark mesal triangles; genitalia, fig. 
75, with penis lobes hook shaped at apexes. 
FEMALE.—Length of body 22-24 mm., of 
fore wing 20-22 mm. Colored much as in 
male, but generally lighter, some individuals 
almost completely yellow, darkest individuals 
ATROCAUDATA 
Vol. 26, Art. 1 
a 
~ 
Fig. 72.—Hexagenia rigida, dorsal aspect 
of head of nymph. 
Fig. 73.—Hexagenia recurvata, penis lobes. 
Fig. 74.—Hexagenia rigida, penis lobes. 
Fig. 75.—Hexagenia limbata, penis lobes. 
Fig. 76.—Hcxagenia munda, penis lobes. 
Fig. 77.—Hexagenia atrocaudata, penis lobes. 
Fig. 78.—Hexagenia bilineata, penis lobes. 
never so dark as darkest males; fore wing 
usually lacking discal spots; hind wing, figs. 
84, 85, without discal spots, posterior margin 
with or without brown band, this band, 
when present, discontinuous. 
NympH.—Length 23-30 mm. _ Frontal 
process of head dome shaped, fig. 69. 
Known from the Mississippi and Missouri 
river valleys, eastern states, and southern 
Canadian provinces. Develops in a great 
variety of waters: small to large creeks, 
small to large rivers, small lakes, and bodies 
of impounded water. 
Illinois Records.—Specimens, collected 
from June 4 to September 15, are from 
Anna, Antioch, Beardstown, Bloomington, 
Carbondale, Champaign, Channel Lake, 
Decatur, Dixon, Elgin, Fisher, Fox Lake, 
