PHILIP A. MUNZ 29 



4. Decrease in the number of postnodals. — In the Zygoptera this 

 tendency comes in much later than does the reduction in the ante- 

 nodal series, nor does it ever reach so advanced a state. It ap- 

 pears very marked in the Coenagrioninae only, and there in the 

 Argia and Coenagrion series some of the highest genera such as 

 Diargia (fig. 85), Agriocnemis (fig. 104), Hemiphlebia (fig. 106), 

 and others have very few postnodals. 



5. Loss of the cross-veins in the quadrangle and subquadr angle. — 

 The number of cross-veins in and before the subquadrangle seems 

 generally to correspond roughly to that of the antenodals. In 

 those Agrionidae with numerous antenodals the subquadrangle is 

 generally crossed and the number of "cubito-anal" cross-veins is 

 so great that Ac itself is distinguished only with difficulty. Neo- 

 charis (fig. 31) offers an interesting exception; in it the antenodals of 

 both series are numerous, but there are no true cross-veins back of 

 Cu. Diphlebia (fig. 34) and Amphipteryx (fig. 35) may also have 

 none. In the Coenagrionidae the lack of cross-veins in the sub- 

 quadrangle has become the normal state and it is only in such 

 forms as Paraphlebia (fig. 64) and Dimeragrion (fig. 67) that any 

 are found. The same tendency is true of the cross-veins of the 

 quadrangle; they are first lost in the Epallaginae and in the higher 

 forms are normally retained by one genus only, Anomisma (fig. 48). 



6. Reduction in number of those antenodal cells situated between Mi 

 and Cui. — As shown by Dr. Calvert "this character is -in general 

 dependent on the degree of retraction of the nodus," and, "a reduc- 

 tion in the number of antenodal cells may occur independently of 

 retraction of the nodus, however, by the greater development of 

 the quadrilateral distad." It is evident also that this reduction is 

 a part of the general tendency toward a smaller number of cross- 

 veins in the wing as a whole; almost any part of which when ob- 

 served through a long ascending series, will show the cross-veins 



* becoming placed further apart. Other examples of the tendency 

 might be noted, for instance, the freeing of the basal radial space 

 where the latter exists. 



7. Reduction in the number of cross-veins behind the anal vein. — 

 In part this is in line with the general tendency to drop out cross- 

 veins; in part due to progressive petiolation which reduces the 



MEM. AM. ENT. SOC, 3. 



