PLECOPTERA OF NORTH AMERICA 



17 



Fusions between principal veins, eliminating the cross- 

 veins that normally stand between occurred in all 23 times 

 and in 17 of the 28 specimens, in a single wing of a speci- 

 men 13 times; in front wings 6 times; in hind wings 16 

 times; between veins Rs and M 7 times; between veins 

 M and Cu 13 times; between the branches of vein M 3 

 times. 



Variation in Perla varians. — Walsh, the describer of 

 this species, noted its remarkable variability and gave it 

 an appropriate name. We have had no long series of 

 specimens from any single locality, and have used seven 

 specimens collected together at one time at Elkhart, Ind., 



Sc 



4thA 



3dA 



5thA 

 Fig. 3. Wings of Perla various Walsh. 



for the study of just a few wing characters con- 

 nected with the cord. The radial sector was 3-branched 

 in 25 of the 28 wings, two branched (had a single fork) 

 in the other two. 



It has been noted by every one that this species tends 

 to preserve a cell adjacent to the cord in the space be- 

 tween veins Rs and M. The variation in respect to extra 

 crossveins in this space is as follows : 



