l\t fnnadiaii Jutomolajbt. 



Vol. XL. LONDON, NOVEMBER, 1908. No. ir, 



A KEY TO THE NORTH AMERICAN SPECIES OF AESHNA 



FOUND NORTH OF MEXICO. 



BY E. M. WALKER, TORONTO. 



Although nearly two years have elapsed since the writer commenced 

 a critical study of the North American species of the Odonate genus 

 Aes/uia, Fabr., it will be some time yet before the work is completed. 

 This delay has been chiefly due to the length of time required for the 

 execution of the numerous illustrations and for obtaining a proper field 

 knowledge of the various species, and also to difficulties experienced in 

 collecting and rearing the nymphs. 



This being the case, it was decided to issue in advance an analytical 

 key to the species treated in the revision in order that, in the interval, 

 species may be listed or otherwise referred to under the names employed 

 therein. 



It has been necessary to draw up a separate key for the determination 

 of the females, as the chief diagnostic characters of the males are found 

 in the superior appendages and accessory genitalia. This key to the 

 females is largely artificial, and it has been very difficult to find reliable 

 characters for the separation of some of the species, although with experi- 

 ence they can almost always be recognized at a glance. Of some of the 

 species I have seen very few females, and it is very probable that with 

 sufficient material some of the characters used will prove invalid. 



A few of the terms employed in the key require special notice. The 

 terms hamular process and hamular fold designate respectively the more 

 superficial and deeper parts of the anterior hamules, and are sufficiently 

 well indicated in figs. 2 and 3 on the plate. 



As the colour pattern is of the same type throughout the genus as 

 represented in North America, it has been found convenient to apply 

 special names to the different bands and spots which characterize this 

 pattern. 



The name dorsal thoracic band requires ro explanation. The first 

 and second lateral thoracic bands are two oblique pale bands on the sides 

 of the mesepimeron and metepimeron respectively. The names used to 



