541 



fourth and fifth postnodal cross-veins hi the front wing and between 

 three and four in the hind wing. 



Abdomen bhie and black ; terga largely blue, with black spots on 

 the base of the first and the apices of 2-6 inclusive, all of the dorsum 

 of seven blue except a basal interrupted ring, and all of ten blue; 

 terga eight and nine blue; sterna 3-8 with mesal lines of black from 

 the cephaHc to near the caudal margins; anal appendages (Figs. 189, 

 196) short, pale, the superiors bifid, the two arms ecjual in length; 

 dorsal arm of the superior appendages black at the tip and forming 

 a blunt hook ; ventral arm pale and nearly straight ; inferior appendages 

 pale, dark at the tips and about as long as the superiors. 



Female. — Color, black and yellow or blue. 



Head similar to that of the male, the blue, however, sometimes 

 replaced by yellow. 



Thorax similar to that of the male; mesostigmal plates as shown 

 in Figure 227. 



Abdomen with broad dorsal stripes on segments 2-10, the stripes 

 contracted to the meson on the bases of terga 3-7 inclusive, and 

 widened subapically on segments 2-7, the widened portion not reach- 

 ing the lateral margins; first tergum pale, with a black spot at the 

 base; sterna 1-8 with black median stripes; ovipositor of the usual 

 form and not reaching caudad of the tenth segment, the ventral mar- 

 gins of the lateral valves feebly serrate. 



Measurc7ncnts 



Length, $ 29 mm. 



Length, 2 29 mm. 



Length of abdomen, S 23-25 mm. 



Length of abdomen, 9 24 mm. 



Length of hind wings, S 16-17 mm. 



Length of hind wings, 9 18 mm. 



Width of hind wing.s, S 4 mm. 



Width of hind wings, 9 4 mm. 



The anal appendages of the male distinguish the species from 

 closely allied members of the genus, and the mesostigmal plates of the 

 females are also characteristic. 



Described from a number of males from Illinois in the collection 

 of the State Laboratory of Natural History, and from females in the 

 collection of E. B. Williamson. 



