May, 1953 
and one-half times as long as second, fourth 
segment twice as long as broad; caudal fila- 
ments white, basal five or six articulations 
stained with red-brown. 
NYMPH, MALE.—Length of body 6-8 mm. 
Head and dorsum of thorax dark brown; 
thoracic sternum white; legs white, all fem- 
ora almost completely shaded with brown, 
fore tibia and tarsus brown, middle and 
hind tibiae shaded with brown at bases, tarsi 
darkened at apexes; tergum of abdomen uni- 
formly dark brown, sternum also usually 
uniform brown, but basal sternites some- 
times lighter brown toward meson; each gill 
with median, black trachea only; median 
caudal filament two-thirds to three-fourths 
as long as cerci. 
Holotype, male. — Vandalia, Illinois, 
April 16, 1946, Mohr & Burks. Specimen 
dry, on pin. 
Paratypes.—ILLINoIS.—Same data as for 
holotype, 1¢. Port Byron: May 15, 1942, 
Ross & Burks, 8¢. Specimens in alcohol. 
Numerous specimens of nymphs collected at 
both above localities, along with adults. 
22. Baetis brunneicolor McDunnough 
Baetis brunneicolor McDunnough (19255:173). 
Mate.—Length of body 6.0-6.5 mm., of 
fore wing 6.5—7.5 mm. Head brown, lighter 
at lateral angles of frontal shelf; each an- 
tennal scape brown, pedicel tan, flagellum 
tan at base, shading to yellow at apex. 
Thorax dark brown, marked with yellow or 
tan at anterior apex of mesoprescutum, at 
posterior ends of outer parapsidal sutures, 
on mesoscutellum, on pleural sutures, and 
on sternal sutures; legs with all coxae yel- 
low-brown, fore leg light yellow-brown, 
middle and hind legs white, often with 
femora faintly stained with tan; wings hya- 
line, veins Sc and R, of fore wing usually 
stained with pale yellow, stigmatic crossveins 
numerous, anastomosed; hind wing, fig. 283, 
with third longitudinal vein long, marginal 
intercalaries present between veins 1 and 
2, and 2 and 3. Abdominal tergites 2-6 
brown, sternites tan; apical tergites opaque 
brown, sternites yellow-brown; genitalia 
pale tan, of the intercalaris type, with a well- 
developed anteromesal tubercle on each first 
forceps segment; caudal filaments pale tan 
at bases, white distad. 
Known from Illinois and Ontario. 
Burks: THE Mayr tiers oF ILLINOIS 135 
Illinois Records. — DunpgE: May 23, 
1939, Burks & Riegel, 1 6. Havana: Mat- 
anzas Lake, Nov. 5, 1939, Ross & Burks, 
Dud. 
23. Baetis intercalaris McDunnough 
Baetis intercalaris McDunnough (1921:118). 
Baetis lasallei Banks (1924:425). 
McDunnough (1938:25) stated that in- 
tercalaris and lasallei were so close as 
scarcely to warrant a separation. I have 
studied types of both species at the Museum 
of Comparative Zoology, and find no char- 
acters that serve to separate the two. 
Mate.—Length of body 4.0-4.5 mm., of 
fore wing 4.5-5.0 mm. Head very dark 
brown, antennae brown, each becoming yel- 
low toward tip of flagellum; eyes in life red- 
tan. Thorax very dark brown to black, 
with yellow-tan on lateral margins of meso- 
notum, at wing bases, and lateral margins 
of mesosternum; all coxae brown, legs other- 
wise white; wings hyaline, veins Sc and R, 
of fore wing stained with faint yellow near 
bases, stigmatic crossveins numerous, anas- 
tomosed marginal intercalaries in  sub- 
costal interspace extremely long, fig. 285; 
hind wing, fig. 284, with marginal inter- 
calaries present, and with third longitudinal 
vein short. Abdominal segments 2-6 snow- 
white, black spiracular dots present; apical 
tergites dark chestnut brown, sternites 
creamy white; genitalia, fig. 297, white, 
mesoapical papilla of first forceps segment 
well developed; caudal filaments white. 
Known from Connecticut, Illinois, Indi- 
ana, Maryland, New York, Ontario, and 
Pennsylvania. This is by far the commonest 
Illinois Baetis. 
Illinois Records.—Atto Pass: May 14, 
1940, Mohr & Burks, 1¢. Ampoy: Green 
River, July 7, 1939, Mohr & Riegel, 12. 
CEDARVILLE: May 26, 1938, Ross & Burks, 
1¢. Des Prarnes: Fox River, May 26, 
1936, H. H. Ross, 1¢. FReeEport: at light, 
June 10-11, 1948, Burks, Stannard, & 
Smith, 29. KANKAKEE: Kankakee River, 
June 6, 1935, Ross & Mohr, 12; June 29, 
1939, Burks & Ayars, 16; July 21, 1935, 
Ross & Mohr, 16; Aug. 1, 1933, Ross & 
Mohr, 1¢; Aug. 16, 1938, Ross & Burks, 
14; at light, July 9, 1948, Ross & Burks, 
36. Miran: Rock River, June 4, 1940, 
Mohr & Burks, 1¢. Momence: June 15, 
