PHILIP A. MUNZ 35 



primitive or of a specialized state in"botli groups, but of one in the 

 first, and of the other in the second. 



8. Change in length of the quadrangle. — At first thought the 

 elongation of the quadrangle seems to be a tendency which may 

 point to departure from the ancient condition and which occurs 

 rather often. F'urther investigation, however, fails to permit of 

 the selection of any very well marked series in which this can be 

 traced. Apparent elongation may be due to narrowing of the 

 quadrangle itself or retraction of the nodus so that the quadrangle 

 almost reaches its level. -Beginning with Climacobasis (fig. 6) 

 and Echo (fig. 7) and proceeding to Psolodesmus (fig. 16), one 

 can observe some elongation, and likewise with Pseudophaea (fig. 

 21), Dysphaea (fig. 22), Anisopleura (fig. 25) and Rhinocypha 

 (fig. 26), and in some Megapodagrioninae the tendency is similar. 

 But for the whole suborder it has perhaps been rather dift'erent; 

 the highest Coenagrionidae have almost as short a quadrangle 

 as Pseudophaea (fig. 21), in fact often they may seem to have a 

 smaller one, partly because of distal obliquity and the resulting 

 shortness of the upper side. The length of the quadrangle, then, 

 does not greatly change, except in short series. 



9. Attachment of supplementary sectors. — Here again is a tendency 

 not at all universal in its appearance, but occuring often enough to 

 deserve mention. Among the Polythorinae it is evident in Chal- 

 copteryx (fig. 4) ; among the Agrioninae it begins in Neurobasis 

 (fig. 14) and Phaon (fig. 17) and ends in Vestalis (fig 18); in the 

 Coenagrionidae, Thaumatoneura (fig. 51) exhibits it to a certain 

 degree, Megaloprepus (fig. 46),' Microstigma (fig. 47) and Anomisma 

 (fig. 48) to a higher one, but since in Pseudostigma (fig. 49) and 

 Mecistogaster (fig. 50) almost all secondary sectors drop out, the 

 tendency cannot longer manifest itself; nor can it in the (\)ena- 

 grioninae. 



10. Straightening of the longitudinal veins. — Wherever there are 

 many supplementary sectors present, the princii)al veins tend to 

 curve, especially near the margin of the wing. But when these 

 sectors drop out the veins themsehes become straight and scarcely 

 curv^e. Among the Agrionidae, this is true of Micromerus (fig. 28) 

 and Philoganga; among the Coenagrionidae of Lestes (fig. 44), 



MEM. AM. ENT. SOC, .V 



