328 



AN INTRODUCTION TO ENTOMOLOGY 



A. Anal area of the fore wings with two or more series of cross-veins (Fig. 



3760). p. 328 Pteronarcid^ 



AA. Anal area of the fore wings with not more than a single series of cross- veins, 

 usually with no cross-veins beyond the basal anal cell. 

 B. Media of the fore wings separating from radius gradually, the two forming 



a sharp angle (Fig. 376^), p. 328 Perlid^ 



BB. Media of the fore wings separating from radius abruptly, the two form- 

 ing a blunt angle (Fig. 376c). 

 C. Anal area of the fore wings with a forked vein arising from the basal 

 anal cell (Fig. 376a). Cerci vestigial, p. 330. Nemourid^ 

 CC. Anal area of the fore wings with only simple veins arising from the 

 basal anal cell (Fig. 376d). Cerci well developed, p. 330 



CAPNIIDiE 



Family PTERONARCID.E 



This is a small family which is represented in North America by 

 only two genera and by but few species. 



Pteronarcys. — This genus includes the largest of our stone-flies. 

 Figure 374 represents a common species. The venation of the wings 



Scr Sr, 



4+\ 





Fig. 376a. — Wings of Pteronarcella badia. 



is reticulate ; the reticulation is irregular and extends in the fore wings 

 from the costa through the anal area. 



A remarkable feature of members of this genus is that vestiges of 

 tracheal gills are retained by the adults. 



Pteronarcella. — This genus includes smaller species than the pre- 

 ceding one, and the venation of the wings is more regular than in 

 Pteronarcys (Fig. 376a). 



Family PERLID.^ 



The members of this family differ from the Pteronarcidae in the 

 smaller number of cross-veins in the anal area of the fore wings, 



