318 
by the writer in a small stream at Dun- 
raven Pass, Mount Washburn, Yellow- 
stone National Park, Wyo., Aug. 2, 1940. 
In addition to five male and two female 
adults, two nymphs and one exuvia were 
collected under such conditions that I am 
certain these immature forms belong with 
the adults. A nymph is shown in fig. 92. 
The adults agree very well with the 
original description and a dissection of the 
apical abdominal sternite of one male re- 
vealed the forked chitinous process of the 
aedeagus which is so characteristic of this 
species and was illustrated by Needham 
& Claassen. Several illustrations of im- 
portant structures of the male and female 
are presented to aid future recognition of 
this little known species, fig. 93. 
NYMPHAL MANDIBLES ——_ 
SN —_— 
v 
NYMPHAL MAXILLA 
ADULT HEAD 
_ AND PRONOTUM 
ea cits 
2) 
si ; 
CG’ ABDOMINAL STERNITES 
3 ABDOMINAL TERGITES 
Fig. 93.—Isoperla fusca. 
Ittinois NATURAL History SURVEY BULLETIN 
Vol.-22;-Areme 
Since the nymph has not been previous- 
ly recognized, a description and illustra- 
tion of it are presented here. 
Nympu. — General color brown with 
lighter areas as in fig. 92. Legs, antennae, 
anal cerci and ventral parts of body pale 
yellow. Short, stout, spinelike setae, in 
addition to longer hairs, present on body 
and particularly femora. Ocelli in same 
relative position as in adult. Basal seg- 
ments of mouthparts not extending notice- 
ably from the sides of the head. Labium, 
maxillae and mandibles as in fig. 93. 
Pronotum broader than long with a pale 
yellow longitudinal stripe in middle, fig. 
93. 
Abdominal tergites mostly dark brown, 
but a pale median longitudinal stripe is 
present, and a lateral flanking stripe on 
each side is slightly in evidence. 2 
Cerci long, many segmented, segments 
progressively longer from base to apex; 
small, stout, spinelike setae encircling apex 
of each segment, but with no evidence of 
long, fine setae on dorsal surface of apical 
segments as in some species. 
Approximately mature specimens with 
a body length of 10 mm. 
No thoracic, anal or submental gills. 
Nymphal specimens collected at same 
time and place as adults. 
Isoperla longiseta Banks 
Isoperla longiseta Banks (1906c, p. 337). 
Original description, @. 
Isoperla longiseta is a species apparently 
associated with the prairie and plain states 
mostly west of the Mississippi River and 
partially replaced in the Rocky Mountain 
and perhaps entirely in the West Coast 
states by mormona Banks. The collection 
of specimens of this species in Missouri by 
Dr. H. H. Ross in 1937 and the determr 
nation as this species of material from 
Ames, Iowa, in 1935, indicated it migh’ 
some day be found in western Illinois 
This supposition was confirmed in 193° 
by the capture in extreme western Illinois 
on the Mississippi River at Quincy, of : 
single female of this species. I am incline: 
to believe that the record of longiseta fron 
“Indiana” by Needham & Claassei 
(1925) was in error. | 
The two typic females, No. 11,336 
the collection of the Museum of Comparé 
tive Zoology, have been studied and com 
