. Bulletin. Natural history; Natural history. 80 ILLINOIS NATURAL HISTORY SURVEY BULLETIN Vol. 21, Art. 3 femur and at base of each tibia. Antennae and cerci brown. Head scarcely wider than pronotum; three ocelli arranged in a triangle, and lateral ocelli closer together than to median ocellus and slightly closer to each other than to inner margins of compound TIPS OF SUBGENITAL PLATES 5 ABDOMINAL STERNITES Fig. 65.—Acroneuria perplexa. Pronotum, fig. 65, approximately quad- rangular, much broader than long, hind angles rounded, front angles rather sharp, rugosities arranged in a defini
. Bulletin. Natural history; Natural history. 80 ILLINOIS NATURAL HISTORY SURVEY BULLETIN Vol. 21, Art. 3 femur and at base of each tibia. Antennae and cerci brown. Head scarcely wider than pronotum; three ocelli arranged in a triangle, and lateral ocelli closer together than to median ocellus and slightly closer to each other than to inner margins of compound TIPS OF SUBGENITAL PLATES 5 ABDOMINAL STERNITES Fig. 65.—Acroneuria perplexa. Pronotum, fig. 65, approximately quad- rangular, much broader than long, hind angles rounded, front angles rather sharp, rugosities arranged in a definite pattern and corresponding well with color pattern a in nymph ; median longitudinal depressed area narrow. Wings long, extending well beyond tip of abdomen ; membrane hyaline with veins dark brown; venation somewhat variable in regard to numbers of cross-veins but otherwise essentially typical for the genus, several cross-veins in forewing in area be- yond the cord, and veins 9-11 of hind wing reaching margin of wings variable. Abdomen, fig. 65, without special struc- tures except for terminal segments. Tenth tergite not cleft; genital hooks prominent, recurved upwards, narrow for most of length and tapering to a point; small spin- ulae numerous on ninth and tenth tergites; ninth sternite with a small, slightly trans- versely oval padlike disk. Two groups of gill remnants are on the side of each thoracic segment and on upper part (usually concealed) of subanal lobes, thus correlating with gills of nymph. Length to tip of wings 27 mm.; lengtli to tip of abdomen 18 mm. FEMALE.—In general very similar to the male as here described, but somewhat larger. Differs from male in important characters as follows: eighth abdominal sternite, fig. 65, with posterior margin somewhat produced over ninth sternite, in most specimens with posterior margin of subgenital plate rounded but sometimes slightly truncate or notched. Holotype, female.—Petersburg, Ind., White river: June 16, 1936,
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