511 



postnodals in the front wing and between the fourth and fifth in the 

 hind wing, usually nearer the fifth; stigma surmounting a single cell; 

 paraptera dull velvety black. 



Abdomen blue aftd black ; basal half and a spot on the sides of the 

 first tergum black, the remainder blue ; dorsum and apex of the second 

 black, the lateral margins blue ; basal rings, and lateral marginal stripes, 

 extending one-half to three-fourths the length of segments 3-6, in- 

 clusive, blue ; the remainder of these terga, black ; tergum seven except 

 a small basal ring, black; dorsum of terga eight, nine, and ten blue, 

 the lateral margins sometimes darker ; first sternum with a black, me- 

 dian spot, 3-10 entirely black; anal appendages short, black, the in- 

 feriors longest and bifurcate (Figs. 149, 150). 



Female. — Color, brown and black. 



Head : front, vertex, occiput, and postgenae dull brown. 



Thorax brown, the mesostigmal plates usually black and the 

 caudal margins forming a thin blade which projects dorsad; black 

 spots present on the mesopleural and metapleural sutures adjoining 

 the wing bases ; legs similar to the male except that the hind pair are 

 almost entirely pale brown. 



Abdomen dull brown, with indistinct touches of blue, very similar 

 to that of the male except that the basal rings are not as broad or as 

 well defined; terga 6-10, inclusive, entirely dull brown; anal appen- 

 dages short; ovipositor long and slender, extending caudad of the anal 

 appendages, pale brown in color. 



Measurements 



Length, $ 30-40 mm. 



Length, 9 34 mm. 



Length of abdomen, $ 24-27 mm. 



Length of abdomen, $ 27 mm. 



Length of hind wings, $ 18-19 mm. 



Length of hind wings, 9 21 mm. 



Width of hind wings, $ 4—4.5 mm. 



Width of hind wings, $ 5 mm. 



Described from a large series of males and females in the col- 

 lection of Mr. E. B. Williamson. 



This species has been reported from Illinois. 



Argia tibialis (Rambur) 



Nymph. — Color, very dark brown. 



Head about as long as broad, pentagonal; eyes black; antennae 

 with all segments except the last two dark on the basal three-fourths. 



