May, 1953 
for the eastern states should be referred to 
leukon. Develops in large and moderate- 
sized rivers. 
Illinois Records.—Specimens, collected 
June 9 to September 24, are from Bloom- 
ington, Champaign, Cleveland (Rock River), 
Como (Rock River), Dixon (Rock River), 
Golconda, Havana, Homer, Kankakee, Lyn- 
don (Rock River), Mahomet (Sangamon 
River), Milan, Muncie, Oakwood, Proph- 
etstown, Rock Island, Rockton (Rock 
River), Roscoe (Rock River), Savanna 
(Mississippi River), Sterling (Rock River), 
Urbana, West Salem, and Wilmington. 
2. Ephoron album (Say) 
Baetis alba Say (1824:305). 
Polymitarcys albus (Say) in part. 
Eaton (1883:47). 
Mavre.—Length of body 9-12 mm., of 
fore wing 8-11 mm. Vertex of head light 
yellowish, shaded with purplish gray be- 
tween ocelli; entire dorsum of thorax light 
cream colored, almost white, sutures faintly 
shaded with tan; legs white to pale yellow, 
with each fore femur and tibia stained with 
purplish gray; abdomen snow-white, apical 
tergites faintly yellowish; genitalia, fig. 67, 
with penis lobes having lateral angles acute, 
slightly upcurved. Each cercus stained with 
gray near base, blending into snow-white 
toward apex. 
The nymph was described by 
(19484: 12). 
Known from the north-central and north- 
Edmunds 
western states. Develops in large and 
moderate-sized rivers. 
Illinois Records.—Fostrer: Mississippi 
River, July 11, 1939, B. G. Berger, 22. 
KANKAKEE: at light, Aug. 4, 1936, Frison & 
murks, 26; Aug: 15, 1938, H.. H:. Rass, 
1g; Aug. 16, 1938, Ross & Burks, 3¢. 
Momence: at light, Aug. 5, 1938, Burks & 
Boesel, 1 6 ; Aug. 16, 1938, Ross & Burks, 
256. PropHETSTOWN: July 7, 1925, T. H. 
Frison, 5¢. St. CHaARLEs: Fox River, July 
8, 1948, Ross & Burks, 1 ¢. WHILMINGTON: 
at light, Aug. 3, 1937, Ross & Burks, 18 ¢. 
EPHEMERINAE 
The subfamily Ephemerinae, as defined 
here, corresponds to the family Ephemeridae 
in Ulmer’s classification (1933:198). It in- 
Burks: THE Mayr ties oF ILLINOIS 35 
cludes the genus Hexagenia, whose members 
are the largest and commonest of Illinois 
mayflies. They are also the most important 
mayflies in the state when considered as 
food for the fishes of our larger lakes and 
streams. 
In the adults, the middle and hind legs 
are well developed and functional. The 
marginal intercalary veins of the wings are 
not netlike. The cubital intercalary veins of 
each fore wing consist of two to four long, 
slightly sinuate, forked veins attached to 
Cu, and extending to the wing margin, figs. 
27, 40, 46. The median caudal filament 
may be well developed, greatly reduced, or 
vestigial. 
In the nymphs, figs. 2, 48-50, the frontal 
process is well developed and the mandibular 
tusks are strong. When the nymph is alive, 
the gills are held curved over the abdominal 
tergites. 
KEY TO GENERA 
ADULTS 
1. Fore wing with crossveins at and posterior 
to bulla crowded and darkened so as to 
form a path extending half way across 
WUT Dae Coe Gp teen eee 5. Ephemera 
Fore wing with crossveins in region of 
bulla not so arranged as to form a path 
extending across wing, figs. 27, 40...2 
Median caudal filament reduced but rela- 
» tively well developed; in female, med- 
ian caudal filament four-fifths to five- 
sixths as long as each cercus; in male, 
one-fifth to one-sixth as long as cercus 
Bare ere Geter sys 6. Pentagenia 
Median caudal filament vestigial: in each 
sex, reduced to only four to nine small, 
poorly defined segments.7. Hexagenia 
i) 
Nympus 
1. Head with a more or less dome-shaped 
anterior projection between bases of 
antennas Nes 405 OO—/2> wena mdiee te 
Rene CRRA Rte ee one 7. Hexagenia 
Head with a two-pronged anterior pro- 
jection between bases of antennae, 
Hie Set De SO ease det ee ee Ae oe 2 
oe Mandibular tusk with dorsolateral angle 
smooth, rounded, fig. 50..5. Ephemera 
Mandibular tusk with dorsolateral angle 
carinate and toothed, fig. 49......... 
Sa RPS Nh eS At ete Paar 6. Pentagenia 
5. EPHEMERA Linnaeus 
Ephemera Linnaeus (1758:546). 
The adults are large, relatively slender- 
bodied mayflies, usually with spotted wings 
