PLECOPTERA OF NORTH AMERICA 



157 



surface rugose. Legs brown, first two tarsal segments 

 short, third segment at least twice as long as one and 

 two combined. Wings subhyaline to dark fumose, with 



a yellow costal margin ; costa, 

 subcosta and costal crossveins 

 lemon yellow, the other veins 

 brown ; subcosta reaches to or 

 nearly to the cord; six or more 

 costal crossveins before the tip 

 of subcosta and several beyond; 

 radial sector usually with three 

 branches ; anal field of hind wing 

 large; Rs-M stem long; several 

 cubital crossveins. Cerci long 

 and slender, the middle seg- 

 ments four to five times as long 

 as wide. 



Male. Ninth abdominal ster- 

 nite much produced and rounded 

 behind ; tenth tergite entire and 

 posteriorly produced into a 

 rounded lobe; subanal lobes 

 modified into upturned, slender, 

 finger-like processes. 



Female. Subgenital plate some- 

 what produced, truncate and 

 medially notched. 



Genotype, Perl a placida Hagen. 

 Distribution. — East of the Rocky 

 Mountains. 



There is a single species. There is considerable varia- 

 tion in the color of the wings and in the color pattern on 

 the head. This has given rise to the description of eight 

 species and varieties within this genus. Long series of 

 specimens collected at the same time and place contain all 

 the variable coloration and color patterns described under 

 these species, but structurally they are all identical. 



Fig. 20. Perlesta placida Hag 



