PLECOPTERA OF NORTH AMERICA 



51 



shaped supra-anal process (sim- 

 ilar in plan to that of Pteronar- 

 cella) lies more or less com- 

 pletely concealed. Backwardly 

 directed processes, set in oppo- 

 sition to the genital hooks are 

 developed in D. vagans on the 

 dorsum of segment 7. A pair of 

 slender stylets is attached to 

 its sides near the bottom of the 

 bend in the U. These characters 

 cannot be seen without dissec- 

 tion ; nor can the large penis, 

 which lies concealed below these 

 parts in the enlarged ventral 

 portion of the 9th segment. 



Short winged forms occur in 

 the several species, and as 

 usual, the wings are most ab- 

 breviated in the males. 



Genotype, Dictyopteryx micro- 

 cephala Pictet (European). 



Key to the species of Perlodes.* 



1. Costal crossveins in com- 

 plete series 2 



Costal crossveins absent 

 for a fourth or more of 

 the distance from the humeral crossvein to the 

 cord 4 



Fig. 12. Perlodes signata Hag. 



Apical crossveins in cubital area numerous 



dolobrata 



Apical crossveins in cubital area few or wanting 3 



Frontal tubercles more or less crescentic tibialis 



Frontal tubercles round bradleyi 



Base of the radial sector joins vein Rl by a 

 rounded curve 4 



Base of the radial sector straight, meeting vein 

 Rl at a very acute angle 5 



*P. minor Kip., from Arctic America, unknown to us, omitted. 



