THE NORTH MIERICAN DRAGONFLIES (ODONATA) OF 

 THE GENUS MACROMIA. 



By Edward Bruce Williamson, 



Of Bluff ton, Indiana. 



All the North American dragonflies referred in the past to 

 Macromia and Eyoplithalmia are congeneric and should be referred 

 to Macromia. DidyTnoys is very close to Macromia, and adequate 

 venational characters for separating the two genera have not been 

 detected. At the same time Didymops seems distinct enough by 

 other characters, and the well-known North American species, 

 transversa, is not discussed in this paper. I have seen only males of 

 Azuma and Epoplithalmia and of but one species of each. They 

 are separated at once from Macromia, among other characters, by 

 the greatly developed genital hamules in the male and by several 

 venational characters, among which may be mentioned the abrupt 

 apical curving of M3 and M4 in both front and hind wings, and the 

 posterior widening of the hind wing from the anal angle to the ter- 

 mination of M4. (See figs. 1, 2.) Venational differences between 

 Azuma and EpopTithalmia are slight and are mainly to be found in 

 the relations of Cu and A in the front wing proximal to the triangle. 

 The crossed or uncrossed condition of triangles and subtriangles, 

 which has been used in the past in distinguishing Macromia and 

 EpopTithalmia has no value here as a generic character. 



The American species of Macromia are distributed generally over 

 the United States and southern and eastern Canada. So far as I 

 know, M. illinoiensis is the only species frequentmg lakes as well 

 as streams. The four species other than illinoiensis which I have 

 seen in life prefer the larger streams, along which they course with 

 swift flight at slight elevation, though they not infrequently leave 

 the streams and pass out of sight over the tallest trees. They are 

 most active during bright days, from about 9 or 10 a. m. till 3 or 4 

 p. m. At Sandusky, Ohio, where illinoiensis has been taken in 

 large numbers, many collect toward evenmg in the cedars on 

 Cedar Point, several individuals frecjuently choosing the same twig 

 for a resting place. It is probable that during the day these indi- 



Proceedings U.S. National Museum, Vol. 37— No. 1710. 

 Proc.N M. vol. 37— 09 24 ob9 



