May, 1953 
3. Frontal process of head dome shaped, fig. 
(SAO) teicher 3. limbata 
Frontal process of head angled on meson 
at apex, figs. 68, 71, 72 
4. Mid-tarsal claw slender, long, fig. 79; 
frontal process of head bluntly angled 
siete: 5. rigida 
Mid-tarsal claw broadened near base, figs. 
80, 81; frontal process of head as in 
THIS (Ole ey WRN rete eae Mae ta ee oes cod 5 
5. Frontal process of head relatively narrow, 
and with straight lateral margins, fig. 
71; mid-tarsal claw slender near tip, 
Imig, Sallie Oa Ss er eee eee 4. munda 
Frontal process of head wider, and with 
curved lateral margins, fig. 68; mid- 
tarsal claw thick near tip, fig. 80...... 
Se pes EO Oe eee 2. bilineata 
1. Hexagenia atrocaudata McDunnough 
Hexagenia atrocaudata McDunnough 
(1924: 92). 
Mave.—Length of body 22-24 mm., of 
fore wing 23-25 mm. Eyes large, almost 
contiguous on meson of head. Dorsum and 
sternum of thorax mostly very dark red- 
brown, pleura with yellow and light red 
areas. Fore wing hyaline, with all veins 
and crossveins very dark red-brown, costal 
interspace red-brown, no conspicuous, discal, 
dark spots present; hind wing, fig. 83, hya- 
line, veins and crossveins dark, no discal, 
dark spots present, outer margin with a 
broad, purplish or reddish-brown band. 
Abdominal tergites mostly dark red-brown, 
with small, yellowish streaks or spots on 
dorsal meson and at lateral margins; gen- 
italia, fig. 77, with short and blunt penis 
lobes. 
FEMALE.—Length of body 23-25 mm., of 
fore wing 24-25 mm. Colored much as in 
male, but brown areas slightly smaller and 
lighter colored; wings as in male. 
NympH.—Length of mature specimen 25 
mm. Frontal process of head, fig. 70, trun- 
cate at apex and with a small mesal indenta- 
tion. 
Known from Georgia, Illinois, Indiana, 
Maryland, Michigan, Missouri, New York, 
North Carolina, Ohio, Ontario, Pennsyl- 
vania, Virginia, and West Virginia. De- 
velops in relatively cool, rapid creeks and 
smaller rivers. “ 
Illinois Records——Momence: Aug. 21, 
1936, Ross & Burks, 1? ; Aug. 22, 1936, 1¢. 
RicHmonp: Aug. 15, 1938, Ross & Burks, 
1¢. Witmincron: at light, Aug. 6, 1947, 
Burks & Sanderson, 29. 
Burks: THE MaAyertigs or ILLINOIS 39 
2. Hexagenia bilineata (Say) 
Baetis bilineata Say (1824: 303). 
Hexagenia bilineata falcata Needham 
(1929292. pla si) hie 162) 
Mavre.—Length of body 14-20 mm., ol 
fore wing 14-18 mm. Eyes separated on 
meson of head by a space one-half as wide 
as width of one eye. ‘Thorax mostly red- 
brown; fore wing hyaline, veins red-brown, 
crossveins darker, several prominent, brown 
spots in disc of wing, costal interspace tinted 
with red-brown; hind wing, fig. 82, with 
several prominent, discal, brown spots. Ab- 
domen, when viewed from side without 
magnification, appears to have two parallel, 
longitudinal, dark brown bands; penis lobes, 
fig. 78, beaked. 
FEMALE.—Length of body 18-22 mm., of 
fore wing 20-22 mm. Color of body and 
wings as in male, but generally slightly 
lighter; parallel, longitudinal, color bands 
of abdomen not so obvious. 
NympuH.—Length 25-35 mm. _ Frontal 
process of head, fig. 68, relatively broad, 
with curved margins; mid-tarsal claw thick 
near tip, fig. 80. 
Known from the District of Columbia, 
Mississippi River valley, Maryland, and 
Virginia. Develops usually only in large, 
relatively slow rivers, but sometimes de- 
velops also in impounded bodies of water. 
Illinois Records.—Specimens, collected 
from June 6 to September 16, are from 
Alton, Cairo, Decatur, Elizabethtown, Ful- 
ton, Glendale, Grafton, Hardin, Harris- 
burg, Havana, Kankakee, Mahomet, Mere- 
dosia, Milan, Monticello, Mound City, 
Murphysboro, Oregon, Peoria, Pontiac, 
Prophetstown, Quincy, Ripley, Rockford, 
Rock Island, Rockton, Rosiclare, Savanna, 
Springfield, Venedy Station, and Wilming- 
ton. 
3. Hexagenia limbata (Serville) 
Ephemera limbata Serville in Guérin 
(1829: 384; pl. 60, figs. 7-9). 
Palingenia occulta Walker (1853:564). 
Palingenia viridescens Walker (1853:550). 
Baetis angulata Walker (1853: 564). 
Hexagenia variabilis Eaton (1883:55). 
Hexagenia venusta Eaton (1883: 54). 
Hexagenia mingo Traver (1931b: 597). 
Hexagenia pallens Traver (1935a: 271). 
Ma te.—Length of body 16-21 mm., of 
fore wing 13-19 mm. The compound eyes 
separated on meson by a space slightly nar- 
