May, 1953 
female specimen, almost certainly a sub- 
imago. The species pwella can probably 
never be identified with certainty. For the 
present, the name primus may be used for 
the species. 
Mare.—Length of body 10-14 mm., of 
fore wing 9-12 mm. Body of living specimen 
snow-white, with wings white and costal 
margin of each fore wing faintly shaded with 
bluish gray. Antennae and apical tarsal 
segments of each fore leg shaded with bluish 
gray. 
Fore leg with femur and tibia approxi- 
mately equal in length, first tarsal segment 
5iA 
53¢ 
Burks: THe Mayr ies or ILLINoIs 29 
one-third as long as tibia, second to fifth tar- 
sal segments equal in length, each twice as 
long as first segment; longer of two tarsal 
claws as long as fifth tarsal segment, shorter 
claw two-thirds as long as longer one. 
Middle and hind legs greatly reduced, but all 
parts still represented by small, membranous 
vestiges. Genitalia, fig. 60, with two charac- 
teristically broad, flat penis lobes. 
FEMALE.—Length of body 13-17 mm., of 
fore wing 16-22 mm. Body of living speci- 
mens snow-white, but often with a faint, 
longitudinal band of grayish brown on 
meson of pronotum and on dorsum of ab- 
52A 
Fig. 514.—Hexagenia limbata, gill of first abdominal segment. 
Fig. 51B.—Hexagenia limbata, gill of fourth abdominal segment. 
Fig. 51C.—Hexagenia limbata, gill of seventh abdominal segment. 
Fig. 524. —Ephoron leukon, gill of first abdominal segment. 
Fig. 52B.—Ephoron leukon, gill of fourth abdominal segment. 
Fig. 52C.—E phoron leukon, gill of seventh abdominal segment. 
Fig. 53A.—Potamanthus myops, gill of first abdominal segment. 
Fig. 53B.—Potamanthus myops, gill of fourth abdominal segment. 
Fig. 53C.—Potamanthus myops, gill of seventh abdominal segment. 
Fig. 544 .—Pentagenia vittigera, gill of first abdominal segment. 
Fig. 54B.—Pentagenia vittigera, gill of fourth abdominal segment. 
Fig. 54C.—Pentagenia vittigera, gill of seventh abdominal segment. 
