1893.] NATURAL SCIENCES OF PHILADELPHIA. 379 



numbered as 3, 5, 6 and 8, and from the genera, in addition to the 

 legionary differences, as follows: 



From Megalestes by 9. 



From Archilestes by 1, 2, 4, 7 and 10. 



From Lestes by 1. 



From Sympycna by 1, 4, 7, 11 and 12. 



From Platy lestes by 1. 



Additional differences from Megalestes and Platylestes may exist, 

 as I have not seen examples of these two genera. 



Other details of generic structure in Ortholestes are : the absence 

 of supplementary sectors between the ultra-nodal and the principal, 

 although the last one or two intervening cells may be divided. 

 Archilestes, Lestes and Sympycna also agree here. 



Between the ultra-nodal and nodal sectors are two or more sup- 

 plementary sectors which are quite broken and form an irregular 

 net work with 4-8 marginal cells. In Archilestes, Lestes 1 and Stjm- 

 pycna there are usually but two supplementary sectors between 

 ultra-nodal and nodal; they are quite distinct and regular; the 

 upper one commences 1-2 cells before the lower one and is usually 

 unbruken (Lestes and Sympycna) or somewhat broken (Archilestes) ; 

 the lower one is usually much broken ; the number of marginal 

 cells between nodal and ultra-nodal is 3-6. 



The ultra-nodal sector arises at about the level of the fifth or 

 sixth post-cubital, and therefore at about one-third the length of the 

 post-cubital series. In Archilestes, Lestes and Sympycna, the same 

 sector more usually arises near the middle of that series. 



Two to eight marginal cells may be present between the nodal 

 and subnodal sectors, depending on the degree of development of 

 supplementary sectors. 



The supplementary sectors between the subnodal and median sec- 

 tors are much broken. 



The basal postcostal cross-vein is placed distinctly nearer the 

 level of the second than of the first ante-cubital ; the reverse is usu- 

 ally the case in Archilestes, Lestes and Sympycna. These relations 

 may be stated in another way by saying that in Ortholestes the first 

 ante-cubital lies but little beyond half way from the base of the 



1 The statements here made for Lestes are based on the following 17 species; 

 unguiculata, uncata, disjuntia, forcipata, inequalis, vigilax, reclangularis, for- 

 ftcula, curina, congener, and tenuata of North America; viridis, nvvipka, sponsa, 

 *virens and barbara of Europe ; Colensonis of New Zealand. 



