68 Ittrnors NarurAt History SurvEY BULLETIN 
on outer sides of coxa and near apex of 
femur; wings hyaline, with brown stain at 
bases, principal veins light yellow. Ab- 
dominal tergum dark red-brown, usually 
with a pair of yellow, submedian spots at 
anterior margin of each tergite, occasional 
specimens with a dorsal, median, longitudi- 
nal, yellow stripe; sternites light red-brown, 
with transverse yellow area near anterior 
margin of each sternite; four minute, black 
marks on each sternite; genitalia, fig. 131, 
yellow-brown, with smoky brown shading 
toward apexes; caudal filaments uniformly 
gray-brown, articulations not darkened. 
FemMALe.—Length of body 7-8 mm., of 
fore wing 8-9 mm. Color in general lighter 
than in male, with dark red-brown areas of 
male being replaced by yellow-brown. En- 
tire sternum of thorax and abdomen yellow, 
faintly shaded with brown near apex of 
mesosternum; fore leg yellow, with brown 
shading near apex of femur; wings faintly 
brown at bases; caudal filaments very light 
yellow, basal articulations red. 
NympH.—Length of body 6-8 mm., of 
caudal filaments 3.5-4.5 mm. Color ex- 
tremely variable, ranging from an almost 
uniformly dark brown form to a form with 
a light yellow, or white, longitudinal, mesal 
stripe that extends from vertex to tenth ab- 
dominal tergite; lateral margins of prono- 
tum and abdominal segments usually light 
yellow or white; caudal filaments usually 
with narrow, brown crossbands throughout 
their lengths. 
Head and thorax without dorsal tu- 
bercles; maxillary palps well developed, fig. 
168; each tarsal claw with 8 to 10 denticles; 
each fore femur with stout, blunt spines 
along posterior margin and near apex, fig. 
161; posterolateral angles of abdominal seg- 
ments 3-9 produced and spinelike; tergites 
2-8 each with a pair of long, submedian 
tubercles, these forming two almost parallel 
rows; caudal filaments bearing long setae in 
apical areas. 
Known from Illinois, Indiana, Maine, 
Michigan, New York, Nova Scotia, and 
Quebec. Develops in cool, fairly rapid creeks 
or small rivers. 
Illinois Records——Aroma Park, Kan- 
kakee River: June 11, 1947, B. D. Burks, 
44,32. Eppyvitre, Lusk Creek: April 4, 
1946, Burks & Sanderson, 4 N; May 24, 
1946, Mohr & Burks, 1 N; May 16-17, 
Vol. 26, Art. 1 
1947, B. D. Burks, 1 6,2 9, 1N. Kanxa- 
KEE, Kankakee River: April 30, 1931, T. H. 
Frison, 45 N; April 23, 1935, Ross & Mohr, 
5 N; May 17, 1935, H. H. Ross, 9 N; July 
Fig. 173.—Ephemerella argo, mature nymph, 
dorsal aspect. 
21, 1935, Ross & Mohr, 14. Momence, 
Kankakee River: June 4, 1932, Frison & 
Mohr, 74 ; May 26, 1936, H. H. Ross, 44 ; 
May 17, 1937, Ross & Burks, 24 N; June 
1, 1937, B. D. Burks, 14; May 15, 1938, 
Ross & Burks, 8 N; May 21, 1940, Mohr 
