200 
excavated base, fig. 392; the penis lobes are 
fused at the meson, on the ventral side, and 
bear a cluster of thin, somewhat convoluted 
laminae at the apexes. 
The nymphs are not known with certainty, 
but fig. 394 shows an extremely rare form 
that may be a nymph of this genus. Only 
three specimens of this form have been col- 
lected in Illinois over a period of more than 
20 years. It has not yet been possible to 
rear it. 
This supposed nymph of Anepeorus has 
the head extremely broad and flat, with the 
compound eyes located near the posterior 
margin; the anterior and lateral margins 
bear a dense fringe of hair; the mouth-parts 
are evidently those of a predator, as the 
mandibles have long, slender incisors, and 
the broad, grinding, molar surfaces are 
absent; the fanglike structure of the maxil- 
lae and labium clearly fits them for pre- 
dacity. The pronotum has lateral, flange- 
like projections; the legs are flattened and 
have a dense fringe of long hairs along the 
posterior margins of all femora and the 
middle and hind tibiae; the anterior margins 
of the femora bear dense fringes of shorter 
hairs; the claws are long, slender, and eden- 
tate; the wingpads show the _ heptageniid 
pattern of veins. The abdomen is flattened 
dorsoventrally and is relatively broad; the 
tergites are clothed with dense, somewhat 
woolly hairs; each of the first seven abdom- 
inal segments has a pair of ventral gills, 
fig. 394, which are all of the same general 
shape; the apex of the terminal abdominal 
segment is produced as a broad lobe; the 
three caudal filaments are all of approxi- 
mately equal length, and their length is 
greater than that of the entire head and 
body; the caudal filaments are virtually 
bare, each clothed with short, sparse setae 
only in the basal area. Both male and female 
specimens have been collected, the male 
nymph showing the rudimentary forceps at 
the posterolateral angles of the projecting 
lobe on the posterior margin of the terminal 
abdominal sternite. 
The short, thickset abdomen and the shape 
of the terminal abdominal sternite elimi- 
nated this nymph from consideration as the 
possible naiad of the genus Pseudiron. The 
nymph here considered to be that of A nep- 
eorus bears a superficial resemblance to the 
nymph of the Russian Behningia ulmeri 
Lestage (Behning 1924: Chernova 1938). 
I-tiInois NaturAL History SurvEY BULLETIN 
Vol. 26; Arti a 
Anepeorus simplex (Walsh) 
Heptagenia simplex Walsh (1863:204). 
Mayflies of this species are almost identi- 
cal in appearance with those of two other 
heptageniid species: Heptagenia persimplex 
and Stenonema integrum. In both persim- 
plex and integrum, however, the fore tarsus 
in the males is much longer than the fore 
tibia. A. simplex is actually an extremely 
rare species, and some of the published rec- 
ords of it have been based on misidentified 
specimens. 
I agree with McDunnough (1929:179) 
that the Walsh specimen in the Museum of 
Comparative Zoology now labeled lectotype 
of this species is not simplex as defined by 
Walsh himself. There is another male spec- 
imen in the type lot at the M.C.Z. which 
is, in my opinion, the true simplex, as it 
agrees closely with Walsh’s original de- 
scription. The abdomen is, unfortunately, 
lacking from this specimen; so I was not 
able to examine the genitalia when I saw 
the specimen in 1942. I am basing my treat- 
ment of the species on McDunnough’s re- 
description (1929:179), based on a single 
pair, now in the Illinois Natural History 
Survey collection, which was collected on the 
Rock River a few miles upstream from Rock 
Island, and on a single male subimago from 
Mount Carmel, on the Wabash River. 
Mate.—Length of body 6-8 mm., of fore 
wing 7-9 mm. Head faintly suffused with 
pink, almost white; antennae white; eyes 
greenish yellow in life, according to Walsh. 
Entire thoracic notum a very faint yellowish 
pink; pleura and sternum white. Legs white, 
with yellow or brown shading on entire fore 
femur, at apexes of middle and hind femora, 
at bases of all tibiae, at apex of fore tibia, 
and at apexes of all tarsal segments; wings 
hyaline, with crossveins in costal half of 
each fore wing stained tan; three to five 
costal crossveins basad of bulla in fore wing, 
seven or eight stigmatic crossveins present 
in each fore wing. Abdomen white; genitalia, 
fig. 392, faintly yellow, caudal filaments 
white. 
FEMALE.—Length of body 7-9 mm., of 
fore wing 8-10 mm. Coloration identical 
with that of male, except that yellow-brown 
shading of each fore femur is confined to a 
middle stripe and small area at apex; ab- 
domen yellowish (due to color of eggs), 
posterior margin of terminal abdominal 
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