. Bulletin. Natural history; Natural history. 154 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 Gills on seventh abdominal segment platelike and bearing tracheae which possess lateral branches, figs. 3256", 328C, 329C 5 Front of head incised on meson, so as to expose a portion oflabrum when viewed from dorsal aspect . .44. Cinygmula Front of head not incised on meson, labrum not exposed dorsaliy 6 (iills of first and seventh pairs enlarged, converging beneath abdomen to form, with intermediate gills, an adhesive disc, fill. 390; fibrillar portion of each gill dorsal, fig. 324 4
. Bulletin. Natural history; Natural history. 154 Illinois Natural History Survey Bulletin Vol. 26, Art. 1 Gills on seventh abdominal segment platelike and bearing tracheae which possess lateral branches, figs. 3256", 328C, 329C 5 Front of head incised on meson, so as to expose a portion oflabrum when viewed from dorsal aspect . .44. Cinygmula Front of head not incised on meson, labrum not exposed dorsaliy 6 (iills of first and seventh pairs enlarged, converging beneath abdomen to form, with intermediate gills, an adhesive disc, fill. 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, 329. 7 7. 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. . 45. Cinygtna Mandibles without a chitinized lobe basad of molar area, fig. 326; platelike components of first and seventh gills subequal in length, fig. 325 42. Heptagenia 41. STENONEMA Traver Stcnonema Trayev (1933fl:173). Most of the American species in the genus Stenonema were formerly placed under the. 329A Fig. 327>1.—Epeorus sp., gill of first abdominal segment. Fig. 327fi.—Epeorus sp., gill of fifth abdominal segment. Fig. 327C—Epeorus sp., gill of seventh abdominal segment. Fig. 328-4.—Cinygmula sp., gill of first abdominal segment. Fig. 328fi.—Cinygmula sp., gill of second abdominal segment. P'^- —Cinygmula sp., gill of seventh abdominal segment. Fig. i29A.—Cinygma integrum, gill of first abdominal segment. (After McDunnough.) Fig. 7)29R.—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.). Plea
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