May, 1953 
pletely fused on the meson; each arm of 
the forceps has three segments. ‘The 
nymphs, fig. 55, are sprawlers, with the 
gills extended laterally. The median caudal 
filament is well developed in the nymphs and 
in the adults of both sexes. 
Adult specimens of Potamanthus should be 
studied when freshly killed, as the faint 
56 
Burks: THE MaAyrties or ILLINOIS 31 
myops. In the Museum of Comparative 
Zoology there is a specimen labeled as the 
type of myops, but it was collected a year 
after the description was published and 
cannot, therefore, be the type. It is, how- 
ever, a specimen determined as myops by 
Walsh himself, and is in agreement with 
the present-day concept of the species. 
Fig. 56.—Potamanthus verticis, dorsal aspect of head of adult male. 
Fis. 57.—Potamanthus myops, dorsal aspect of head of adult male. 
Fig. 58.—Potamanthus distinctus, dorsal aspect of head of adult male. 
color markings fade rapidly after death. 
This fading occurs much more rapidly in 
alcoholic than in dried specimens. 
Reliable specific characters for the nymphs 
of this genus have not been found. 
KEY TO SPECIES 
ADULTS 
1. Abdomen usually entirely unmarked, 
occasionally each abdominal segment 
with a faint, minute, pink spot on either 
side; crossveins in fore wing hyaline in 
each sex; compound eyes of male small, 
TMP Meret VB, Peace Nie ets 1. myops 
Abdomen with large, well-marked, lateral, 
salmon-pink spots or stripes......... 2 
2. Abdomen with lateral stripes; fore wing 
in each sex with black crossveins; com- 
pound eyes of male moderate in size, 
shots Sheps Da se aang ae eee 3. distinctus 
Abdomen with lateral spots........... 3 
3. Female with crossveins of each fore wing 
black, male with those crossveins hy- 
aline, or with only a few of the anterior 
crossveins black; compound eyes of 
Malerlarees Nees IOm nei. ons 2. verticis 
Both male and female with all crossveins 
of each fore wing black; compound eyes 
of male small, as in fig. 57, i 
hon BE hee 5 ea eae ae 4. neglectus 
1. Potamanthus myops (Walsh) 
Ephemera myops Walsh (1863: 207). 
Potamanthus medius Banks (1908:259). 
A study of the type of medius leaves no 
doubt in my mind that it represents the 
same species as the one we have been calling 
Mare.—Length of body 10-13 mm., of 
fore wing 11-14mm. Compound eyes small, 
fig. 57; wings completely hyaline, with no 
crossveins black; abdomen without lateral, 
salmon-pink spots or stripes, or, rarely, with 
small, faint, lateral spots discernible in 
living specimens; caudal filaments with ar- 
ticulations usually slightly darkened with 
red-brown or pink. 
FEMALE.—Length of body 11-13 mm., of 
fore wing 12-14 mm. Eyes same size as in 
male; wings with no crossveins black; ab- 
domen without lateral, salmon-pink spots or 
stripes; caudal filaments with articulations 
usually slightly darkened with red-brown or 
pink. 
Known from Illinois, Indiana, Iowa, Kan- 
sas, Michigan, and Wisconsin. Develops in 
large and moderate-sized rivers. 
Illinois Records.—Adult specimens, col- 
lected June 6 to August 17, are from Aurora 
(Fox River), Champaign, Dixon (Rock 
River), East Dubuque (Mississippi River), 
Effingham, Freeport, Galesburg, Homer, 
Kankakee, Monmouth, Monticello, Muncie, 
Oakwood, Oregon, Peoria, Rockford, Rock 
Island, Rockton, Sterling, and Urbana. 
2. Potamanthus verticis (Say) 
Baetis verticis Say (1839:42). 
Ephemera flaveola Walsh (1862:377). 
The type of Say’s species is lost, but both 
male and female types of Walsh’s species 
