PLECOPTEKA OF NORTH AMERICA 



13 



crossveins and in part from angulated portions of longi- 

 tudinal veins. The basal one comprises the humeral 

 crossvein at the front, the arculus and cubito-anal cross- 



5th A ^^^"^ 4thA 



Fig. 1. Diagram of wing venation in the Plecoptera. The principal 

 veins are designated by letters: C=Costa, $c=Subcosta, 

 R — "Radius, M=Media, C?M=Cubitus, Jr=Anal, Es=radial sec- 

 tor, the principal branch of the Radius. A pins sign between 

 letters i?idicates these veins are fused together. The more 

 typical crossveins are designated as follows: fe — humeral 

 crossvein, r^inter-radial crossvein, ?--w=radio-median cross- 

 vein, m — median crossvein, m-cu — m edio-cubital crossvein, 

 Ctt-a=cubito-anal crossvein. Other veins and areas are des- 

 . ignated as follows: flrc=arculus which is a crossvein to which 

 is often added a deflected basal portion of either of the 

 veins it connects; sfc=:stigma, a thickening in the costal space 

 beyond the tip of the sub-costal vein; a=anal cell; int=m- 

 ter-radial cell; CORD=the cord, a line of transverse join- 

 ings, composed of crossveins and the bases of principal 

 forks, extending from the stigma obliquely backward to the 

 cubital vein. The broad area bounded externally by the cord 

 is sometimes spoken of as the wing disc. 



veins in the middle and the crossvein that delimits the 

 anal cell at the rear. The outer line of bracing is called 

 the transverse cord (or, more briefly, simply the cord). 



