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[LLINoIs NATURAL 
History Survey BULLETIN 
Vol. 26, Art. 1 
Fig. 894. —Neoephemera purpurea, elytroid gill. 
Fig. 89B.—Neoephemera purpurea, gill of first abdominal segment. 
Fig. 89C. —Neoephemera purpurea, gill of fourth abdominal segment. 
Fig. 904 —Tricorythodes atratus, elytroid gill. 
Fig. 90B.—Tricorythodes atratus, gill of sixth abdominal segment. 
Fig. 90C.— 
Tricorythodes atratus, gill of fourth abdominal segment. 
Fig. 914.—Caenis sp., gill of first abdominal segment. 
Fig. 91B.—Caenis sp., elytroid gill. 
Fig. 91C.—Caenis sp., gill of sixth abdominal segment. 
Fig. 91D.—Caenis sp., gill of fourth abdominal segment. 
Fig. 92.—Neoephemera purpurea, claw of middle leg of mature nymph. 
Fig. 93.—Brachycercus lacustris, claw of middle leg of mature nymph. 
Fig. 94.—Caenis sp., claw of middle leg of mature nymph. 
Fig. 95.—Tricorythodes atratus, claw of middle leg of mature nymph. 
Fore wing with relatively numerous cross- 
veins and with median intercalary vein 
extending only halfway to wing base, 
fig. 98; male genital forceps with three 
segments. tp. LOLs... cca te oe aire 
Prosternum twice as broad as long, fore 
coxae being widely separated on venter 
Nes SRR eG ae g 10. Brachycercus 
Prosternum at least twice as long as broad, 
fore coxae being close together on venter 
... 11. Caenis 
Fore wing broadest in the anal region, 
fig. 98; isk ened without hind wing . 
i .9. Tricorythodes 
Fore wing. more “elongate and narrow, 
broadest in the center; subimago with 
UEC DAS he ge a 12. Leptohyphes 
2; 
Mature Nympus 
First abdominal segment without gills; 
each operculate gill borne by second 
abdominal segment triangular, fig. 96, 
or elongate-oval; operculate gills well 
separated on mid-dorsal line of ab- 
domen.. «0500 0c. os 2 
First abdominal segment bearing a pair 
of single, filamentous gills; each opercu- 
late gill borne by second abdominal 
segment semiquadrate, these opercu- 
late gills meeting or overlapping on mid- 
dorsal line of abdomen, figs. ~ 
Operculate gills triangular, fig. 96...... 
So NG DR ae 9. Tricorythodes 
