62 ILLiINoIs NATURAL 
filamentous gills absent on first ab- 
dominal segment.... 
Platelike gills present on abdominal seg- 
ments 4-7, figs. 162-164; filamentous 
gills present on first segment. . 
History Survey BULLETIN 
Vol. 26, Art. 1 
Frontal shelf of head without such a 
notch. 0566. cs ct 8 
8. Frontal shelf with a pair of small, triangu- 
lar, lateral projections, fig. 156 
Fig. 151.—Ephemerella bicolor, head of mature male nymph, anterior aspect. 
Fig. 152.—Ephemerella bicolor, head of mature female nymph, anterior aspect. 
Fig. 153.—Ephemerella temporalis, head of mature nymph, anterior aspect. 
Fig. 154.—Ephemerella cornuta, head of mature nymph, dorsal aspect. 
Fig. 155.—E phemerella walkeri, head of mature nymph, dorsal aspect. 
Fig. 156.—Ephemerella lata, head of mature nymph, dorsal aspect. 
Fig. 157.—Ephemerella cornutella, frontal shelf of head of mature nymph, dorsal aspect. 
2. Fore femur not enlarged and toothed on 
anterior margin, figs. 161, 172, 173. .3 
Fore femur enlarged and toothed on 
anterior margin, fig. 160...5..5...<: 6 
3. Apical half of caudal filaments clothed 
with short spines, fig. 172; maxillary 
palps reduced or entirely wanting, 
fee TOT Nader Cs ee. ok 10 
Apical half of caudal filaments clothed 
with long hairs, fig. 173; maxillary 
palps well developed, fig. 168...... 14 
4. Gill on abdominal segment 4 operculate, 
fig. 164; maxillary palps wanting, fig. 
169 5 
Gill on abdominal segment 4 semiopercu- 
late, figs. 162, 163; maxillary palps 
present, asine. 6S. so ane ee ss 29 
5. Occipital tubercles wanting in male, 
vestigial in female, figs. 151, 152... .22 
Occipital tubercles well developed in both 
sexes, although larger in females than 
i RMIOR OO LON a te oe de oe sk 23 
(WALKERI Group) 
6. Occipital tubercles present, as in fig. 
15 .2. tuberculata 
Occipital tubercles absent............ 
7. Frontal shelf of head with a notch be- 
neath each antennal base, fig. 155. . 
; Bt takes iho delp se ae. Walker 
Frontal shelf with a pair of conspicuous, 
lateral horns, figs. 154, 157.......... 
9. Body of mature nymph 6-7 mm. long; 
frontal horns so curved inward as to be 
almost semicircular, fig. 157.......... 
Se) 
sem ica tal Nh, 8 eae 4. cornutella — 
Body of mature nymph 9-10 mm. long; 
frontal horns not so markedly incurved, 
fe hS4: oy Kc ee 5. cornuta 
(SERRATA Group) 
10. cary pall palps entirely wanting, fig. 
169 a oe 10. deficiens 
Maxillary palps present, although re- 
duced in size, fic. 167) 2) 11 
11. Prothorax with a pair of small, dorsal, 
submedian tubercles near _ posterior 
MALCOM es. ee aoe 8. serrata 
Prothorax lacking dorsal tubercles... .. 12 
12. Head, thorax, and legs clothed with long 
halts. cri oo ae ee 7. sordida 
Head, thorax, and legs not clothed with 
long hairy :.i.. .. 1. +s eee 13 
13. Caudal filaments black at bases, tips 
light yellow or white; each abdominal 
sternite with a pair of dark, lateral 
streaks and a row of four black dots. . 
Sisson an ce Rete 9. serratoides 
Caudal filaments entirely light yellow or 
white, fig. 172; each abdominal sternite 
