106 Intinors NaturAt History Survey BULLETIN 
stigmal crossveins anastomosed ; dorsum of 
body brown, with yellow markings, abdom- 
inal venter almost entirely light yellow or 
white, with a discontinuous, longitudinal, 
brown stripe on meson. Male genitalia, 
Vol. 26, Art. 1 
area milky. Ground color of abdomen light 
tan to almost white, with brown shading; 
each tergite with a broad, transverse, shaded 
area at posterior margin, a large, triangular 
spot near each posterolateral angle, and a 
Fig. 247.—Siphlonurus alternatus, mature nymph, lateral aspect. 
fig. 243, with inner processes elongate, 
finger-like at apexes, and grossly serrate 
on outer margins; outer processes acute at 
apexes, with lateral margins flaring and 
finely serrate; both inner and outer processes 
with numerous, minute spines. 
The nymph is unknown. 
This species is known from Connecticut, 
Massachusetts, Michigan, New Hampshire, 
New York, and Quebec. 
2. Siphlonurus alternatus (Say) 
Baetis alternata Say (1824: 304). 
Baetis annulata Walker (1853: 567). 
Baetis femorata Provancher (1876:267), 
not Say. Misidentification. 
Siphlurus alternans Provancher (1878:127). 
Misspelling. 
Mace.—Length of body 11-13 mm., of 
fore wing 10-12 mm. Head light yellow, 
with brown shading at bases of ocelli, on 
vertex along mesal margin of each com- 
pound eye and on meson, and across frontal 
shelf below antennae; compound eye gray, 
with two light and two alternating, dark 
stripes on outer surface of lower portion; 
antennae tan, each scape slightly darkened 
at base and apex. Thorax tan, with light 
yellow to almost white markings on pleura 
and sternum. Legs light yellow, each with 
brown annulations at base and near apex 
of femur, at base and apex of tibia, and at 
apex of each tarsal segment, all annulations 
narrow except one near apex of femur; 
wings hyaline, veins and crossveins dark 
brown, costal and subcostal crossveins weak, 
stigmal crossveins anastomosed and stigmal 
broad, longitudinal stripe on meson; each 
sternite with a pair of oblique, lateral marks, 
a median spot on anterior margin, and a 
pair of submesal dots in center; genitalia, 
fig. 246, light tan; caudal filaments tan at 
bases, becoming white at apexes, articula- 
tions dark brown. 
FEMALE.—Length of body 11-13 mm., of 
fore wing 12-14 mm. Color pattern as in 
male, but background slightly lighter and 
brown shading less intense; caudal filaments 
almost entirely white, only faintly tan-shaded 
near bases, with articulations chocolate 
brown. Apical margin of terminal abdominal 
sternite produced, nipple-like on meson. 
NympuH.—Fig. 247. Length of body 11-13 
mm., of caudal filaments 6-7 mm. Color 
patterns of thorax, legs, and abdomen very 
similar to those of the adult, but markings 
of abdominal venter somewhat broader than 
in the adult; each gill on abdominal segments 
1 and 2 composed of two equal-sized plates, 
gills on the following segments composed of 
a large plate with a much smaller, recurved, 
dorsal plate, fig. 224; posterolateral, spine- 
like prolongations of tergites darkened at 
tips; each caudal filament with a broad, 
brown crossband near middle and a nar- 
rower crossband at tip. 
Known from Illinois, Indiana, Michigan, 
New York, Nova Scotia, Ontario, Quebec, 
and Wisconsin. 
Illinois Records.—FreeEport: at light, 
June 10-11, 1948, Burks, Stannard, & Smith, 
1g, 32. Rockrorp: Long slough of Rock 
River, May 13, 1927, D. H. Thompson, 1 N. 
(Walsh 1862: 369 records this species from 
