A VENATIONAL STUDY OF THE ZYGOPTERA 



arising just beyond MA; A = first anal vein, Ac = anal crossing, 

 Ab=anal bridge, A' = anal vein from Ac to MA; N= nodus, 

 Sn=subnodus; St=stigma, B.S. =basal space, B.R.S. =basal 

 radial space; An=antenodal cross- veins, Pn=postnodal cross- 

 veins, Ar =arculus, MA =medio-anal link; Q = quadrangle, Sq = 

 subquadrangle. 



/»r. 



Fig. A. Venation of Agrion (Calopteryx). 



These terms are all familiar ones and need for the most part no 

 definition here. The subquadrangle is that space between Ac and 

 MA, and between Cu and A, or Cu and the hind margin of the 

 wing when A' is not present. Ac cannot always be located because 

 of the numerous cross-veins between Cu and A to be found in some 

 genera, but can generally be distinguished by its obliquity. The 

 term medio-anal link is one defined by Mr. Williamson (1913) "as 

 the cross vein forming the distal end of the quadrangle and that 

 part of Cu2 opposed to Cu, and placed transversely to the long axis 

 of the wing." Supplementary sectors are those longitudinal veins 

 present between the principal veins. The quadrangle, subquad- 

 rangle, basal space, and basal radial space are said to be crossed 

 when they have cross veins, and Sive free when without cross- veins. 

 The basal radial space is open when M1+2 does not touch R, and 

 closed when M1+2 fuses with R. Of the antenodals there are two 

 series: those of th.e first or costal series, i.e. those between C and Sc; 

 and those of the second or subcostal series, i.e. between Sc and R. 



