126 
4. Median caudal filament two-fifths as long 
as each cercus......... 20. rusticans 
Median caudal filament three-fifths as 
long as each cercus...... 11. vagans 
5. Gills with prominently darkened, pinnate- 
ly branching tracheae........-----: 6 
Gills either without visible tracheae or 
with at most a single, median trachea 
in each gill, these tracheae never con- 
SPICUOURs Fs 6. COTS sie a aOR 10 
6. Each gill of seventh pair relatively slender, 
with apex pointed............ ert 7 
Each gill of seventh pair oval, with ar 
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Abdominal tergites 2-10 each varie- 
gated with brown and white on disc; 
tergites 5 and 8-10 usually largely or 
enerety white oy 2.25 255 os PF ed sat 
9. Each caudal filament with brown shading 
at base, in addition to dark brown cross- 
bands at middle and at apex........ 
Aas pte Se 2 oa 23. intercalaris 
Each caudal filament white at base, 
darkened only at middle and at apex. . 
Bees tented: utes o Sota: 16. levitans 
10. Abdominal tergites 2-9 each uniformly 
brown on disc, with lateral margins 
white, but tergite 5 usually somewhat 
lighter in color than others; each caudal 
filament shaded with brown in basal 
half, in addition to dark brown cross- 
bands at middle and at apex.......... 
eke cass pat aU cea PCOS outer es 15. pluto 
Abdominal tergites 2-9 more or less varie- 
gated with brown and white, tergites 
5 and 9 mostly or entirely white; each 
caudal filament white or pale cream 
colored in basal half............... 11 
11. Median caudal filament almost as long 
as cerci, at least five-sixths as long.... 
Rid) Relic Os 2 Mind tae ae 17. flavistriga 
Median caudal filament not more than 
three-fourths as long as cerci........ 12 
12. Tenth abdominal tergite entirely white. . 
18. cingulatus 
Tenth abdominal tergite mostly brown, 
white only along anterior margin..... 
25. phoebus 
1. Baetis spinosus McDunnough 
Baetis spinosus McDunnough (1925): 174). 
Mave.—Length of body 4.0-4.5 mm., of 
fore wing 5.0-5.5 mm. Head very dark 
brown to black, yellow-brown at lateral 
Intinois NaturAL History Survey BULLETIN 
Vol. 26, Art. 1 
angles of frontal shelf; each antenna light 
gray-brown, shading to yellow at apex of 
flagellum; eyes in life dark red-brown. Tho- 
racic notum black, yellow-brown along an- 
terolateral margins of mesoscutum, pleura 
and sternum dark brown, light red-brown or 
yellow-brown at wing bases and bordering 
sutures; all coxae brown, each fore leg 
faintly yellow, middle and hind leg white; 
wings hyaline, veins Sc and R, of fore wing 
faintly stained with yellow-brown, stigmatic 
crossveins 7—9 in number, uniformly slant- 
ing, not anastomosed; hind wing with only 
two longitudinal veins, costal projection 
either absent or vestigial. Abdominal seg- 
ments 2-6 white or stained with tan, black 
spiracular markings present; apical tergites 
chocolate brown, sternites white. Genitalia, 
fig. 289, distinctive, second segment of each 
forceps arm with a prominent, apicomesal 
tubercle, fourth segment as long as wide; 
genitalia and caudal filaments white or, 
occasionally, faintly tinged with yellow. 
Known from Illinois, Indiana, Manitoba, 
New York, Ontario, and Quebec. 
Illinois Records.—Aroma Park: Kan- 
kakee River, July 8, 1948, Ross & Burks, 
1¢. Muwncte, Stony Creek: May 24, 1914, 
18; July 3, 1929, Frison & Park, 16% 
Oaxkwoop, Salt Fork River: May 29, 1948, 
B. D. Burks, 14; June 5, 1948, Burks & 
Sanderson, 3%. Princeton: Big Bureau 
Creek, May 23, 1941, Ross & Burks, 1¢. 
PROPHETSTOWN: July 7, 1925, T. H. Frison, 
eae 
2. Baetis propinquus (Walsh) 
Cloe vicina Walsh (1862:380), not Hagen. 
Misidentification. 
Cloe propingua Walsh (1863:207). New name. 
Baetis propinquus (Walsh). Eaton (1871: 121). 
Acentrella propingua (Walsh). Traver 
(1937: 83). 
Baetis dardanus McDunnough (1923:41). 
I have studied the lectotype of propin- 
quus and a paratype of dardanus and I can 
find no specific differences between them; 
McDunnough (19254:172) long ago con- 
cluded that the two species were probably 
synonymous. ; 
Mate.—Length of body 4-5 mm., of fore 
wing 4.5-5.5 mm. Head dark brown to 
black; antennae yellow-brown to tan; eyes 
dark brown. Thorax dark brown to black, 
yellow-brown at anterolateral margins of 
mesoscutum, at apex of scutellum, on pleural 
