May, 1953 
cleptis is smaller, the hind wing is relatively 
wider, the second forceps segment is semi- 
tuberculate, and there is a single acute pro- 
jection between the bases of the genital for- 
ceps in cleptis, in contrast to two small pro- 
jections in this position in erebus. 
Mate.—Length of body 3.5 mm., of fore 
wing 4 mm. Head dark brown, with white 
spot at either lateral margin of frontal 
shelf; each antenna brown, with flagellum 
becoming white toward the apex. Thorax 
dark brown, lighter along dorsal sutures 
and at apex of mesoscutellum; wings hya- 
line, a brown spot at base of each fore wing, 
veins light brown; stigmatic crossveins in 
each of fore wings six or seven in number, 
slanting, not anastomosed, no marginal in- 
tercalaries in Sc interspace; hind wing, fig. 
273, narrow, only one-third as wide as 
long, costal projection hooked, veins 1 and 
2 slightly converging at apexes, a single 
marginal intercalary present between veins 
2 and 3, third vein slightly more than half 
as long as wing; all coxae brown, fore leg 
entirely tan, middle and hind legs white. 
Abdominal tergites 1-6 yellow-brown, ter- 
gites 7-10 slightly darker brown; sternites 
yellow-brown, with lateral margins of ster- 
nite 9 dark brown; black, longitudinal 
tracheal lines at spiracles; genital forceps, 
fig. 293, yellow-brown at bases, graduating 
to very light tan at apexes; first segment 
with rounded anteromesal projection, second 
segment cylindrical, with a suggestion of a 
mesal tubercle at apex, third segment con- 
stricted at base, enlarged toward apex, twice 
as long as second segment, fourth segment 
long, slender, four times as long as wide; 
caudal filaments white, slightly shaded with 
tan in basal area. 
Holotype, male.—Detroit, Illinois, Sep- 
tember 15, 1939, Ross & Mohr. Specimen 
in alcohol. 
Paratype.—Same data as for holotype, 
1g. Specimen in alcohol, wings and geni- 
talia on microscope slides. 
11. Baetis vagans McDunnough 
Baetis vagans McDunnough (1925a: 219). 
Mate.—Length of body 5.5—6.5 mm., of 
fore wing 6.0-7.5 mm. Head dark brown, 
yellow-brown at lateral angles of frontal 
shelf; each antennal scape usually entirely 
yellow, sometimes partly shaded with brown, 
pedicel brown, flagellum gray-tan, shading 
Burks: THE Mayr tiss oF ILLINOIS 131 
Fig. 298.—Baetis vagans, mature nymph, 
to yellow at apex; eyes red-brown. Thorax 
dark brown, marked with yellow-brown at 
anterior and posterior ends of each outer 
parapsidal furrow, at wing bases, along 
pleural sutures, on entire prosternum, and 
on margins of mesosternum; wings hyaline, 
anterior longitudinal veins stained pale yel- 
low, stigmatic crossveins of fore wing nu- 
merous, anastomosed to form a dense net- 
work; hind wing, fig. 280, with prominent 
costal projection, third longitudinal vein well 
developed, and marginal intercalary veins 
present between both veins | and 2, and 2 
and 3; all coxae pale gray-tan, fore leg light 
gray-brown, fore tibia with a darker gray 
spot at apex, middle and hind legs pale yel- 
