555 



tarsi pale, darker at the apices; wings with ten postnodal cross-veins 

 in the front wing and eight in the hind one; Mo arising near the fifth 

 postnodal vein in the front wing and between the fourth and fifth 

 or between the third and fourth, usually near the fourth, in the hind 

 wing. 



Abdomen orange or blue and black ; dorsum of terga i-8 inclusive, 

 black, except interrupted basal rings on 3-7, lateral surfaces of one 

 and two, and the lateral margins of 3-8 ; all of tergum nine and the 

 lateral surfaces of the tenth orange or blue, the dorsum of ten being 

 black; anal appendages (Figs. 185,192) dark brown, the superiors 

 much longer than the inferiors, blunt at the apices, the lateral surfaces 

 convex, the mesal surfaces somewhat concave ; inferiors about half 

 as long as the superiors and subconical, the tips black and directed 

 mesad. 



Female. — Color, pale blue or orange, and black. 



Head similar to that of the male. 



Thorax similar in all particulars to that of the male ; the orange- 

 colored females are, however, less frequent; mesostigmal plates (Fig. 

 214) long, the lateral margins rounded, and a diagonal pale stripe 

 crossing the plates. 



Abdomen blue or orange, and black ; terga 1-9 with black, dorsal, 

 longitudinal stripes from the bases to the apices, the stripes widened 

 near the apex on 2-7 and narrowed on the apex of nine ; lateral surfaces 

 of all terga, basal rings on 3-7, and an apical ring on one, yellow or 

 bluish; all of segment ten yellow or blue; sterna 3-8 black; anal ap- 

 pendages of the usual form ; ovipositor with the lateral valves pale 

 and serrated on the ventral margins, the prostyles brown. 



3Ieasurements 



Length, S 34-35 mm. 



Length, 9 34-35 mm. 



Length of abdomen, S 26-28 mm. 



Length of abdomen, 9 28 mm. 



Length of hind wings, $ 17 mm. 



Length of hind wings, 9 .20 mm. 



Width of hind wings, S 3.5 mm. 



Width of hind wings, 9 4 mm. 



One of the commonest species in Illinois, occurring in all localities. 

 Next to Ischnura verticalis it may be considered as the most abundant. 



The nymphs may be collected in slow streams, permanent ponds, 

 or lakes, and prefer the clear water. They emerge in central Illinois 



