AQUATIC INSECTS 



Fig. 151. — Nymph of Peltoperla; its gills are 

 hidden beneath the flaring thorax. 



Peltoperla. — In Peltoperla the clusters of thoracic gills are 

 entirely concealed under the flaring margins of the thoracic 

 segments (Fig. 151). Fullgrown nymphs are one half inch 

 long. The genus is generally distributed over North Am- 

 erica. Emerging in May-June. 



Fig. 152. — Nymph and adult of Tceniopteryx 

 nivalis, a winter stonefly. 



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