May, 1953 
dominal segments 4-9 slightly produced as 
relatively blunt spines; caudal filaments 
bearing long, dense setae in apical areas. 
Known from Connecticut, Illinois, In- 
diana, Michigan, New Brunswick, New 
Hampshire, New York, North Carolina, 
Pennsylvania, Quebec, South Carolina, Ten- 
nessee, Vermont, Virginia, and West Vir- 
ginia. Develops in fairly large rivers. 
Illinois Records.—Gotconpa: May 13, 
1932, Frison, Mohr, & Ross, 4 N. Mount 
CARMEL: Wabash River, April 2, 1932, 
Frison & Ross, 19 N. 
18. Ephemerella subvaria McDunnough 
Ephemerella subvaria McDunnough 
(19315: 84; 1931d:194). 
Matre.—Length of body 8-9 mm., of fore 
wing 9-10 mm. Head, thorax, and abdom- 
inal dorsum dark brown; abdominal venter 
light red-brown; wings hyaline, with veins 
and crossveins light brown. Genitalia, fig. 
136, with penis lobes broad and with five or 
six stout, basal spines on either side; oc- 
casionally one or two apical, ventral spines 
present also; second forceps segment rela- 
tively straight, with apex suddenly expanded. 
NympH.—Head and thorax entirely with- 
out dorsal spines or tubercles, but abdominal 
tergites with relatively well-developed, sub- 
median spines, fig. 165; each tarsal claw 
with seven to nine denticles; caudal filaments 
bearing long setae in apical regions. 
Known from Michigan, Ontario, Pennsyl- 
vania, Quebec, and Wisconsin. 
19. Ephemerella fratercula McDunnough 
Ephemerella fratercula McDunnough 
(1925a: 213). 
Matre.—Length of body 7 mm., of fore 
wing 8 mm. Thorax and dorsum of terminal 
abdominal segments light brown, basal ab- 
dominal segments dark brown on dorsum; 
venter yellow; wings and wing veins hyaline. 
Genitalia, fig. 129: each penis lobe with two 
or three stout, dorsal spines and seven to 
nine ventral ones; second forceps segment 
almost straight, suddenly enlarged at apex. 
Known from Quebec. 
20. Ephemerella invaria (Walker) 
Baetis invaria Walker (1853:568). 
Mate.—Length of body and of fore wing 
8-9 mm. Head light red-brown, eyes reddish 
Burks: THE MAyr igs oF ILLINOIS 71 
orange. Thorax light red-brown; pronotum 
red-brown, with faint gray shading; thoracic 
sternum dark red-brown; legs light yellow, 
almost white, with apex of each fore femur 
and fore tibia stained with red-brown; 
wings hyaline, longitudinal veins stained 
with light brown. Abdominal tergum smoky 
brown, becoming slightly lighter on apical 
tergites; sternum uniformly yellow-brown; 
caudal filaments white, articulations dark. 
Genitalia, fig. 135, light yellow; each penis 
lobe bearing five to eight stout, dorsal spines 
in basal and lateral positions on either side 
and, in most specimens, a single pair of 
ventral spines at apex, in some specimens, as 
many as four apical spines; second forceps 
segments sharply expanded at apex. 
NymeH.—Length of body 7-9 mm., of 
caudal filaments +5 mm. Color of body 
varying from dark brown with yellow mark- 
ings to yellow with small, brown markings; 
thorax of light-colored specimens usually 
with two brown crossbands; abdominal ter- 
gites 5 and 6, in area between gills, partly 
or almost completely light colored. 
Head and thorax without dorsal tu- 
bercles; maxillary palps well developed; each 
tarsal claw bearing five to seven denticles; 
abdominal segments 4-9 with well-developed, 
stout, spinelike projections at posterolateral 
angles, segment 3 often with rudimentary 
posterolateral spines; minute to obsolescent 
dorsal, submedian spines present on abdom- 
inal tergites 3-9; caudal filaments bearing 
long, dense setae in apical areas. 
Known from Illinois, Maryland, Michi- 
gan, New York, Ontario, Quebec, and Wis- 
consin. Develops in fairly rapid, moderate- 
sized rivers. 
Illinois Records.—D1xon: Rock River, 
May 22, 1925, D. H.. Thompson; 3:'N. 
Orecon: Rock River, May 15, 1930, Frison 
& Ross, 1 N. RockrForp: Rock River, May 
4, 1926, D. H. Thompson, 13 N. Rockton: 
Rock River, May 15, 1926, D. H. Thomp- 
Sone Ne 
21. Ephemerella rotunda Morgan 
Ephemerella rotunda Morgan (1911: 113). 
Ephemerella feminina Needham (1924: 309). 
Mate.—Length of body and of fore 
wing 9-11 mm. Thorax light pinkish yellow, 
with brown markings; abdominal dorsum 
yellow, with a broad, brown crossband on 
each segment; venter light yellow or white 
