14 A VENATIONAL STUDY OF THE ZYGOPTERA 



Coenagrionidae, especially in the position of the base of M3 

 and of Rs and in the petiolation and general arrangement of 

 veins. It connects the Lestinae to the Epallaginae through 

 the genera Psendolestes and Ortholestes, and differs from these forms 

 chiefly in the number of antenodals. On the other hand, the 

 Lestinae are related very closely to the Megapodagrioninae by 

 Rhipidolestes (fig. 52). Yet in this same group of Megapodagrion- 

 inae it is necessary to include Thaumatoneura (fig. 51), which with 

 its number of antenodals and abundant sectors indicates a descent 

 from some Agrionid, possibly one like Philoganga (fig. 36) in which 

 the quadrangle is short, and M3 and Rs arise at some little distance 

 beyond the arculus. The retraction of the nodus in a form like 

 Philoganga would bring about a condition comparable to that in 

 Thatimatoneura, except for the numerous sectors and many cross- 

 veins of the latter. As will be shown later, Thaumatoneura in turn 

 leads to the Pseudostigmatinae and to the other Megapodagrion- 

 inae, which by reduction approach the Coenagrioninae and these in 

 their turn are connected with the Protoneurinae. After this addi- 

 tional evidence is presented, it will be seen that it is a very logical 

 thing to consider the Coenagrionidae merely a specialized offshoot 

 or number of offshoots from the Agrionid ae, as arranged in the 

 tree in Figure C. 



In this connection the following quotation is of interest. Till- 

 yard (1914b) in discussing the classification of the Zygoptera de- 

 clares, "It becomes now more than ever apparent that the Selysian 

 division into Calopterygidae and Agrionidae is quite untenable as a 

 natural dichotomy, more than this, it is pretty clear also that the 

 Zygoptera are not like the Anisoptera, derived from an original pure 

 line descent. Triangle-formation most certainly started once ; and, 

 however far back new fossil discoveries may take us as regards the 

 first formation of the triangle, there can be no doubt about the 

 origin of all Anisoptera from that single line of descent, which 

 Palaeontology already places as far back as the Trias, and which 

 probably began in the Permian period. Most of the Zygoptera 

 (certainly all those with regular quadrilaterals) must have branched 

 away from the Anisoptera-XmQ before this. But who can tell how 



