2 74 Anrials Entomological Society of America [Vol.1, 



Hence, although I was able, through the tracing of lines of 

 specialization, to indicate natural groups, I made no attempt to 

 locate all the genera of the world in these groups, nor to set their 

 precise boundaries. 



The recent magnificent work of Monsieur R. Martin on the 

 Corduliinae of the great de Selys collection^ supplies excellent 

 figures of the venation of ever}^ known genus (as well as figures 

 of the genitalia of most of the species) and is a boon to every 

 w^orker on the Odonata. Naturally, the system of classification 

 used in this work is largely that of de Selys: but M. Martin has 

 furnished in his illustrations and in his key abundant data for 

 a more modern arrangement of the group. As I have had oppor- 

 tunity, I have been studying this data from time to time, com- 

 paring the figures with my own photographs, and drawing up a 

 key to the genera of the world as a means of setting forth a more 

 natural arrangement of the entire group. 



I had these keys before me when Mr. Williamson's recent 

 "Revision of the Classification'^ of the Corduliinae" came to hand, 

 and I have studied this paper with great interest and pleasure. 

 Williamson's arrangement of the genera is a vast improvement 

 over the pioneer arrangement of de Selys; and the improvement 

 grows out of better discernment as to what are the fundamental 

 venational characters. De Selys' primary division of the group, 

 (made, it must not be forgotten, at a time when these characters 

 were little understood), was based upon the presence or absence 

 of crossveins in the supertriangle. These crossveins are always 

 weak and functionally unimportant, and if sometimes fairly con- 

 stant, this is just the sort of character most likely to prove mis- 

 leading at critical points. It was only by too close adherence to 

 this criterion that Aeschnosoma, for example, could be severed 

 from its obvious allies, Somatochlora, etc., and immolated among 

 the coarse Macromians. Williamson abandons the use of such 

 characters (perhaps a little too completely) , and wisely bases his 

 arrangement on the disposition of the principal \'eins of the wing. 

 He arranges the genera in five groups "of approximately co-ordi- 

 nate rank", and demonstrates that the members of each group 

 possess numerous marks of affinity. But he leaves three genera 

 incertae sedis (the three Corduline genera with triangles of the 



4. Collections Zoologiques du Baron Edm. de Selys Longchamps; Cata- 

 loge Systematiqtie et Descriptif. Fascicle XVII. Brussels, 1906. 



5. Entom. News. Vol. 19, pp. 428-431, 1908. 



