553 



Length of abdomen, $ 28 mm. 



Length of abdomen, 9 27 mm. 



Length of hind wings, $ 19 mm. 



Length of hind wings, 9 21 mm. 



Width of hind wings, $ 4 mm. 



Width of hind wings, 9 3.5 mm. 



A species of apparently local distribution, occurring in the lake 

 region of Illinois. Several collections of nymphs and adults were 

 made at Lake Villa, July 13 and 14, 191 5, and a number of adults 

 were reared from the nymphs. 



While closely related to signatum, the nymph shows a great dif- 

 ference in the gills, making it recognizable at sight. It is quite different 

 from the species figured by Walker as pollutum ( ' 1 3 ; pi. 1 , fig. 10), and 

 his description also differs from the specimens obtained at Lake Villa. 



Enauagma signatum (Hagen) 



Nymph. — Color, buff or greenish. 



Head elliptical in outline, the caudo-lateral angles not projecting 

 strongly, but thickly studded with short setae ; first two segments of 

 the antennae dark in color, nearly equal in length, the second slightly 

 shorter, the third longest, and the remaining ones decreasing succes- 

 sively in length ; labium, when folded, extending just caudad of the 

 procoxae, with three mental setae, five lateral, and three or four 

 smaller ones on the margin of the median lobe. 



Thorax : legs light in color except a dark ring on the apical third 

 of each femur and the tips of the third tarsal segments; femora with 

 a few small setae and scattered hairs ; metathoracic wing-cases extend- 

 ing nearly to the fourth abdominal segment. 



Abdomen : the segments of the abdomen appear to have a greater 

 transverse diameter near the apical fourth on account of the projecting 

 lateral keels; the keels are well developed and setose, the setae being 

 grouped mainly at one point near the apex of the keel ; dorsum of 

 segments 4-8 with short apical rows of small, heavy setae, terga 

 nine and ten with longer rows, usually extending onto the venter; 

 sterna two, three, and four with a cluster of small thick setae on the 

 apical third, and the venter with a black line extending from the basal 

 segment to segment nine; gills (Figs. 56, 69) lanceolate, the dorsal 

 marginal setae of the median gill grouped mainly at one point, usually 

 just proximad of the point where the first transverse band reaches 

 the margin; beyond the ventral marginal row of setae the margins 

 of the lateral gills are distinctly emarginate ; the pigmentation of the 



