74 The May-flies and Stone-flies 



BB. Second segment of the tarsi small, shorter than the others, cerci absent. 



C. Veins radiating from the ends of the radial cross-vein forming an X. 



NEMOURA. 



CC. Veins radiating from the ends of the radial cross-vein not forming an X. 



LEUCTRA. 



The genus Perla (Fig. 108) includes more species than any other. The 

 species of Pteronarcys retain gills in the adult condition. The species of 

 Chloroperla are small, delicate, and pale green. Leuctra includes the slender- 

 est of the stone-flies; they are small and brownish. Comstock says that 

 there are several species of stone-flies that appear on the snow on warm 

 days in late winter. They become more numerous in early spring, and 

 often find their way into houses. The most common one in Central New 

 York is the small snow-fly, Capnia pygmcea, which is grayish black. The 

 female is 9 mm. (about f in.) long, with an expanse of wings of 16 mm. 

 (about -f in.), while the male is but 4$ mm. (about \ in.) long, and has 

 short wings which extend but two-thirds the length of the abdomen. 



