118 Annals of the Carnegie Museum. 



now, to apply the expression "forked" to the dark humeral stripe 

 whenever it divides into two diverging branches, one on the humeral 

 suture, the other running up on the mesepimeron. 



I repeat the statement of the ' Biologia ' that the chief specific char- 

 acters are furnished by the abdominal appendages of the males and the 

 mesostigmal laminae of the females, although, owing to the difficulty 

 of describing these structures accurately and briefly, recourse is had 

 chiefly to figures rather than to words in the attempt to make them 

 known. 



Key to South American Species of Argia Mentioned in this Article. 



Males. 



I. Total area of dark colors on abdominal segments 3-6 and thoracic dorsum 

 greater than the total pale area on the same parts. 

 I. Thoracic dorsum not brilliantly metallic. 

 A. Labrum pale. 



B. Pale colors on dorsum of 3-6 limited to a transverse basal ring and 

 at most a fine mid-dorsal line ; rear of head chiefly black. 

 C. Abdominal segment 8 mostly black on dorsum. 

 D (not represented). 



DD Abd. segment 9 mostly black on dorsum, anterior half to 

 fourth of its dorsum pale, superior appendages not bifid 



at tip translata. 



CC. (not represented). 



CCC. Abdominal segments 8 and 9 pale on dorsum. 

 a. (not represented). 



aa. Abd. seg. 3 with the basal sixth or less blue, remainder 

 of the dorsum black, 3 antenodal cells on the hind 

 wings. 

 b. Inferior appendages bifid, abd. segs. 8 and 9 with an 

 inferior longitudinal black stripe each side. 



reclusa. 

 BB. Pale colors on dorsum of 3-6 consisting of a transverse basal ring 

 and a mid-dorsal stripe on some or all of them, tapering pos- 

 teriorly, 8 mostly blue on dorsum. 

 F. Superior appendages distinctly bifid, inner branch much longer 

 than the outer. 

 Rear of head black, black humeral stripe not forked. 



sordid a. 

 Rear of head chiefly pale, black humeral stripe forked in its 



upper h al f to third fosleri. 



FF. Superior appendages variously formed, but not distinctly or 

 deeply bifid. 

 d. Antenodal cells on the front wing usually more than 3. 



