154 
6. 
Ittinois NaturAL History SurRVEY BULLETIN 
Gills on seventh abdominal segment 
platelike and bearing tracheae which 
ossess lateral branches, figs. 325C, 
SINC  BIGE; o23000hik 5s Kee 
Front of head incised on meson, so as to 
expose a portion of labrum when viewed 
from dorsal aspect... .44. Cinygmula 
Front of head not incised on meson, 
labrum not exposed dorsally........ 6 
Gills of first and seventh pairs enlarged, 
converging beneath abdomen to form, 
with intermediate gills, an adhesive 
disc, fig. 390; fibrillar portion of each 
gill dorsal, fig. 324. ..46. Rhithrogena 
Gills of first and seventh pairs not con- 
verging beneath abdomen, gills not 
forming an adhesive disc; fibrillar por- 
tion of each gill ventral, figs. 325, see 
+f 
Vol. 26, Art. 1 
Each mandible with a heavily chitinized 
lobe on mesal margin, basad of molar 
area, fig. 330; platelike component of 
first abdominal gill only two-thirds as 
long as that of seventh gill, fig. 329... 
SMe BE a 45. Cinygma 
Mandibles without a _chitinized lobe 
basad of molar area, fig. 326; platelike 
components of first and seventh gills 
subequal in length, fig. 325.......... 
Lela ee Say 42. Heptagenia 
41. STENONEMA ‘Traver 
Stenonema Traver (1933a:173). 
Most of the American species in the genus 
Stenonema were formerly placed under the 
328C 
330 
Fig. 327A.—E peorus sp., gill of first abdominal segment. 
Fig. 327B.—Epeorus sp., gill of fifth abdominal segment. 
Fig. 327C.—E peorus sp., gill of seventh abdominal segment. 
Fig. 328A.—Cinygmula sp., gill of first abdominal segment. 
Fig. 328B.—Cinygmula sp., gill of second abdominal segment. 
, Fig. 328C.—Cinygmula sp., gill of seventh abdominal segment. 
Fig. 329A -—Cinygma integrum, gill of first abdominal segment. (After McDunnough.) 
_Fig. 329B.—Cinygma integrum, gill of second abdominal segment. (After McDunnough.) 
Fig. 329C.—Cinygma integrum, gill of seventh abdominal segment. (After McDunnough.) 
Fig. 330—Cinygma integrum, mandible of mature nymph. (After McDunnough.) 
