May, 1953 BurKs: 
Tue Mayrties or ILLINoIs 
\) 
101 
230 
Fig. 229.—Siphlonurus marshalli, labrum of mature nymph, dorsal aspect. 
Fis. 230.—Parameletus columbiae, libial palp of mature nymph. 
Fig. 231.—Baetis vagans, labrum of mature nymph, dorsal aspect. 
death, regardless of the method of preserva- 
tion of specimens. The fore wing is typical 
for the subfamily; the hind wing has an 
acute costal projection, and vein M_ is 
forked near the base of the wing, fig. 237. 
The male penis lobes are always separated 
to the base, and the forceps base is deeply 
excavated on the meson, as in fig. 236. The 
apical abdominal sternite of the females has 
a median notch on the posterior margin, 
figs. 238, 239. There are two well-developed 
caudal filaments. 
The streamlined, vigorously swimming 
nymphs, fig. 240B, are distinguished from all 
other known mayfly nymphs by the pecten of 
spines borne by each maxilla, fig. 2404. The 
legs are relatively short, and the tarsal claws 
are uniformly single, nondenticulate, slender, 
and much shorter than the tibiae. The gills 
are single and platelike, each gill having a 
single, stout, rodlike stiffener near each 
dorsal margin and a weaker but otherwise 
similar rod near each ventral margin, fig. 
227. There are three well-developed caudal 
filaments; the cerci bear long, dense setae on 
the inner sides only. 
The genus 4meletus includes 26 Nearctic 
species, 22 of which occur in the western 
states. Two of the remaining four species 
have been taken only in Quebec and Nova 
Scotia. The other two species occur in the 
Midwest and both normally are partheno- 
genetic. Males are unknown for one species 
and only two male specimens of the other 
species are known to have been collected. 
KEY TO SPECIES 
ApuLtT FEMALES 
Venter of abdomen without ganglionic mark- 
ings; terminal abdominal sternite as in fig. 
239; lateral margins of apical sternite 
Bitonithyerinicisedsi ter eah a. oe 2S 1. lineatus 
Venter of abdomen with brown ganglionic 
markings; terminal abdominal sternite as in 
fig. 238; lateral margins of apical sternite 
Siialecl Un eye nests wee sh Seta cate ec 2. ludens 
2a. C2 
232 
Fig. 232.—Siphlonisca aerodromia, male gen- 
italia. 
Fig. 233.—Siphlonisca aerodromia, abdomen 
of adult male, ventral aspect. 
Fig. 234.—Siphlonisca aerodromia, abdomen 
of mature male nymph, ventral aspect. 
