559 



This species was collected at Carbondale, 111., June, 191 5, and 

 was reared at that time. It has not been reported elsewhere in the 

 state but doubtless occurs about glacial lakes and ponds. 



The nymph differs from that of exsiilaiis chiefly in the darker 

 color. In all the specimens studied the labium has only two men- 

 tal setae as compared with three in cxsiilans. The gills show con- 

 siderable difference in the shape and pigmentation, particularly of the 

 apical portions. 



The adult is most closely related to exsiilans, but both sexes may 

 be distinguished by the reduced amount of black on the mesopleural 

 suture, the greater amount of blue on the front, and the exceedingly 

 large postocular spots. 



Genus NkhaIvEnnia Selys 



The nymph of the only representative of this genus occurring in 

 Illinois is characterized by its peculiar type of gills, in which the 

 tracheae are much more numerous near the widest portion of the gill 

 than elsewhere. 



The dominant color of the adult is metallic green or bronze, the 

 mesepisterna being entirely without pale stripes and the pronotum 

 without pale spots. The female has the caudal lobe of the pronotum 

 trilobed and the eighth sternum is without the ventral apical seta. 

 The sternites at the base of the cephalic pair of gonapophyses arc 

 minute and scarcely visible. 



• Nehalennia IRENE Hagen 



Nymph. — Color, brown or green. 



Head oval in outline, the caudo-lateral angles with but few setae ; 

 antennae with the second segment longer than the first, the second 

 segment and proximal third of three dark in color ; labium, when 

 folded, extending nearly to the mesocoxae, with a single large mental 

 seta and a smaller one alongside; lateral setae five, and the lateral 

 margins of the median lobe with about five small setae. 



Thorax: femora and tibiae with rows of sparsely placed setae, 

 the preapical rings of brown on the femora very indistinct; apical 

 tibial scales present ; wing-cases extending nearly to the apex of the 

 fourth abdominal segment. 



Abdomen slender, with feeble lateral keels, the cephalic two or 

 three without setae, the caudal ones with not more than six or seven ; 

 cuticle of the abdomen with small whitish spots on a darker back- 

 ground; gills (Fig. 61) much broader beyond the middle, the lateral 



