May, 1953 Burks: THE Mayrtigs or ILLINoIs 153 
6. Stigmatic area of fore wing with an ir- 
regular, longitudinal line dividing the 
stigmatic crossveins into two rows of 
cellwlessie S22)2 Bias: 45. Cinygma 
Stigmatic area of fore wing not divided 
into two rows of cellules, fig. 318, al- 
though the crossveins are often partly 
OLrreatiy anastomosed. ss so. 2: ek 7 
12. 
width of each less than one-third the 
length. . .41. Stenonema 
Small subapical spine absent; large mesal 
spines robust, greatest width of each 
more than one-third the length, fig. 363 
Beye Baie hte este, SLURS 42. Heptagenia 
Small, mesal subapical spine present, figs. 
SAS A ODO sp GOD ees amy, 41. Stenonema 
Fig. 3244 —Rhithrogena sp., gill of first abdominal segment. 
Fig. 324B.—Rhithrogena sp., gill of fifth abdominal segment. 
Fig. 324C.—Rhithrogeva sp., gill of seventh abdominal segment. 
Fig. 3254 .—Heptagenia diabasia, gill of first abdominal segment. 
Fig. 325B.—Heptagenia diabasia, gill of fifth abdominal segment. 
Fig. 325C.—He ptagenia diabasia, 
gill of seventh abdominal segment. 
Fig. 326.—He ptagenia maculipennis, mandible of mature nymph. 
7. Outer lateral margin of each penis lobe 
with a cluster of spines which may be 
either large, figs. 333-339, or small, fig. 
Orava en eels (os oaklh eee 41. Stenonema 
Outer lateral margin of each penis lobe 
without a cluster of spines.......... 8 
8. Apex of each penis lobe transversely or 
obliquely truncate, with a rounded or 
angulate, apicomesal corner, figs. 331, 
340-347, 349-351, 353-356, 363-366. .9 
Apex of each penis lobe not transversely 
or onliquelysytruncate... o> 40... 12 
9. Apex of each lobe with the mesal angle 
lower than the apicolateral angle, figs. 
655 TAS (5 OS 5 | eee A 10 
Apex of each lobe with mesal angle nearly 
on a level with, figs. 340-346, 349, 351, 
353-356, 363, or higher than, figs. 347, 
350, apicolateral Eis aved (Set ian ea coeeabene 
10. Apical angle of each penis lobe eae a 
cluster of rather large spines, fig. 331.. 
Be Re Rech hae Sone aeas 41. Stenonema 
Apical angle of each penis lobe without 
a cluster of spines, figs. 364-366..... 
2B eege CS a me ee es 42. Heptagenia 
11. Small subapical spine, fig. 104, present at 
apicomesal angle of each penis lobe, 
figs. 340-347, 349-351, 353-356; large 
mesal spines, fig. 10g, slender, greatest 
Small, mesal subapical spine absent, figs. 
366-370, 375, or, if present, greatly en- 
larged as in figs. 374, 376-380........ 
eRe gh EN ciep ees lir Ne 42. Heptagenia 
Mature Nympus 
Second segment of maxillary palp ex- 
tremely long, recurved over dorsum of 
Ghofaxen toss G9 Seas 48. Arthroplea 
Second segment of maxillary palp not re- 
curved over dorsum of thorax....... 2 
Mouth-parts fitted for predatism, with 
maxillae and mandibles fanglike..... 
SEEN Sf he Mer TROL ait 47. ?Anepeorus 
Mouth-parts fitted for a diet of vegetable 
matter or plant and animal detritus; 
each mandible with a broad molar 
ALCAN ES = SLO SSOP tyat ees esa se 6s 3 
Median caudal filament vestigial, fig. 
C01 ORR Uy Peach che opted eae ae 43. Epeorus 
Median caudal filament well developed, 
HES MOUS SOSHO OO ee: Sec eek veh acaee wi 4 
Gills on seventh abdominal segment 
slender and semifilamentous, either en- 
tirely without tracheae or with one, 
two, or three simple tracheae without 
lateral branehess tien so OO! iss sss sna 
