65 Intinors NarurAL History Survey BULLETIN 
Fig. 172. — Ephemerella frisowi, mature 
nymph, dorsal aspect. 
fore femur light brown, fore tibia and tarsus 
and all of middle and hind legs white; wings 
hyaline, with brown stain at base of each 
wing, each fore wing milky in stigmatic area. 
Abdominal tergites 1-7 and anterior half of 
tergite 8 white, usually with a fine, median, 
dorsal, brown line and a pair of small, 
brown, lateral marks on each tergite; pos- 
terior half of tergite 8, and tergites 9 and 
10, light brown; abdominal sternum white, 
usually with a pair of lateral, brown dots 
on each sternite; caudal filaments entirely 
white, articulations not darkened. Genitalia, 
fig. 123, white, with forceps faintly shaded 
with tan. 
NympH.—Fig. 172. Length of body 5.0- 
6.5 mm., of caudal filaments 2.5-3.5 mm. 
General color light yellowish tan, sometimes 
almost white, with small and variable brown 
markings. 
Vertex of head, dorsal area of pronotum, 
and (usually) basal area of front wingpads 
with irregular, light brown markings; apexes 
of femora and bases of tibiae usually shaded 
with light brown; a minute, dark brown 
Vol. 26, Art. 1 
dot present at apicoventral angle of each 
trochanter. Dorsal part of abdominal ter- 
gites fairly uniformly shaded with light 
brown in area not covered by gills, elongate, 
dark brown markings along line of inner 
dorsal margins of gills and on median dorsal 
line; abdominal venter rather uniformly 
shaded with light tan, this shading freckled 
with light yellow or white dots; a minute, 
dark brown dot present near lateral margin 
of each abdominal sternite, these dots form- 
ing a sublateral row on either side of ab- 
dominal venter; basal half of each postero- 
lateral projection of sternites shaded with 
tan; each caudal filament with a single tan 
crossband usually present near base. 
Head and thorax without tubercles; max- 
illary palps present, but somewhat degen- 
erated, fig. 167; each tarsal claw with six 
to eight denticles; posterolateral angles of 
abdominal segments 4-9 produced, bluntly 
pointed; posterior margin of second abdom- 
inal tergite with a pair of extremely small, 
submedian tubercles; tergites 3—7 with these 
tubercles relatively well developed; eighth 
tergite with tubercles greatly reduced, but 
discernible, tubercles wanting on ninth ter- 
gite; pairs of tubercles converging slightly 
from tergites 3 to 7, rudimentary tubercles 
more widely spaced on tergite 8; abdominal 
segments | and 2 without gills, segments 3—7 
bearing platelike gills; caudal filaments with 
relatively few, short setae at each articula- 
tion, these setae not longer nor more dense 
in apical than in basal area of filaments. 
Known from Illinois and Missouri. De- 
velops in fairly rapid creeks or small rivers. 
Illinois Records.—Muwncig, Stony 
Creek: June 8, 1927, T. H. Frison, 1 N; 
May 22, 1942, Ross & Burks, 1¢. Oaxk- 
woop, Salt Fork River: June 6, 1925, T. H. 
Frison, 1 ¢ ; June 9, 1926, Frison & Auden, 
38; May 21, 1928, T. H. Frisomeie 
June 29, 1929, T. H. Frison, 2 N; June 
14, 1935, C. O. Mohr, 6 N; May 21, 1936, 
Mohr & Burks, 3 N; June 11, 1936, C. O. 
Mohr, 9 N; May 22, 1942, Ross & Burks, 
5 N. 
7. Ephemerella sordida McDunnough 
Ephemerella sordida McDunnough 
(1925¢:42; 1931d: 205). 
Mave.—Length of body 4.5-5.0 mm., of 
fore wing 5-6 mm. Body very dark brown, 
almost black, with abdominal  sternites 
