256 PROCEEDINGS OF THE ACADEMY OF [Maj', 



(156. Reduction in the number of rows of cells between Ms and M4.) 



16. Rectangular quadrilateral. 



17a. Reduction in the number of antenodal cells between M4 and 



Cui. 

 (176. Reduction in the number of rows of cells between Mi and Cui.) 

 (18. Reduction in the number of cubito-anal cross-veins.) 

 (19. Reduction in the number of rows of cells between Cui and Cu2.) 

 (20. Reduction in the number of rows of cells posterior to Cu2.) 

 21. More distal petiolation of the wing. 

 (22. Reduction in the number of anal cross-veins.) 



I have endeavored to indicate that the paleontological evidence 

 is not as strong for some of these statements, by enclosing them in 

 parentheses, as for those left unenclosed. There is no ontogenetic 

 evidence as yet. 



These conclusions and the data on which they are based merely 

 permit us to determine the probable course, or direction, of change 

 in certain features of the venation. They do not enable us to decide 

 as to the relative order in which the different features changed, 

 whether, for example in the ancestors of living Podagrionine genera, 

 Ms assumed a position at or distad to the subnodus at an earlier, or 

 at a later, period than the reduction of the number of rows of cells 

 in the area posterior to Cu2 occurred, although, given a character, 

 we can say which genera should come first and which should follow 

 in our phylogenetic list in respect to the modifications of that charac- 

 ter. In the imperfection of our knowledge, we are largely guided, 

 therefore, by motives of convenience in selecting the primary charac- 

 ters on which a classification of the members of this group is to be 

 based. .Having regard to all these considerations, the following 

 scheme for a phylogenetic grouping of the genera of Selys' legion 

 Podagrion is presented. 



Synopsis of Venational Characters of Genera of the Legion 

 Podagrion. 



Legion Podagrion Selys 1862. 



IMs separating from M1+2 nearer to the nodus than to the arculus. 

 Pterostigma normal, i.e., consisting of but a single cell. Cu2 present. 

 Supplementarj' f^ectors present, at least between Mia and M2, except 

 in Perilestes. 



A. — Ms separating from M1+2 proximad to the subnodus, at six- 

 tenths or more of the distance from arculus to subnodus (half-way 

 in Rhipidolestes) . 



