. Bulletin. Natural history; Natural history. 336 ILLINOIS NATURAL HISTORY SURVEY BULLETIN XX:IV cella is apparently restricted to the western part of this continent. Presence of gills on the third abdominal segment readily separates the nymphs of Pter07iarcella from those of Pteroyiarcys. The adults differ in venational characters and in number of pairs of vestigial gills on abdominal segments. Pteronarcys Newman Newman (1838) p. 175. Genotype Pteronarcys regalis Newman ^Pteronarcys dorsata (Say), subsequent designation of Enderlein (1909).. Fig. 269.—Typical large river habitat of Illinois s
. Bulletin. Natural history; Natural history. 336 ILLINOIS NATURAL HISTORY SURVEY BULLETIN XX:IV cella is apparently restricted to the western part of this continent. Presence of gills on the third abdominal segment readily separates the nymphs of Pter07iarcella from those of Pteroyiarcys. The adults differ in venational characters and in number of pairs of vestigial gills on abdominal segments. Pteronarcys Newman Newman (1838) p. 175. Genotype Pteronarcys regalis Newman ^Pteronarcys dorsata (Say), subsequent designation of Enderlein (1909).. Fig. 269.—Typical large river habitat of Illinois stoneflies. The Rock river at Oregon and similar streams within or bordering the state are favored by Acroneuria abnormis, A. ruralis and Pteronarcys nobilis. Pteronarcys nobilis Hagen Figs. 19, 28, 54, 84, 114, 160, 170, 259, 267, 268\ 270, 271, 272, 273, 274, 275. Pteronarcys nobilis Hagen (1861) p. 15. Original description (cf). Our studies reveal only one species of this genus, nobilis Hagen, from Illinois. It was first recorded from our state by Walsh (1862) from Rock Island. In the "Table of Distribution by States" of Needham and Claassen (1925) two species of Pteronarcys are indicated without definite records for Illinois, and in the text dorsata (Say) is stated to be "common in small rivers of the central ; The two species thus indicated are undoubtedly dorsata and nobilis. Material in the collection of Cornell university has no actual specimens of dorsata from Illinois. Adults of these gigantic stoneflies are essentially nocturnal and by day hide under bridges or other objects that offer fair protection from light. They have never been observed to feed and structure of the mouthparts indicates that they never do. Lights along watercourses prove attractive to the adults at night, and most of our specimens have been captured as a result. Interestingly enough, adults of all other Illinois genera (Allocap- * Figure numbers in bold face are drawi
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