501 



d. Mo arising between the fourth and sixth postnodal cross-veins 

 in the front wing and between the third and fourth in the 



hind Enallagma. 



dd. Mo arising between the third and fourth postnodal cross-veins 



in "the front wing and between the second and third in the hind. 



e. Dorsum of the fourth abdominal tergum black, except a 



narrow basal ring; stigma of the front wing of the male 



not remote from the margin Isclinura. 



ee. Dorsum of the fourth abdominal tergum orange or yellow 

 with the exception of a basal and apical spot in the male 

 and a small apical spot in the female; stigma of the front 



wing of the male remote from the margin (Fig. 83) 



Anomalagrion. 



Genus Argia Rambur 



The nymphs are characterized by the short thickset form, the 

 abdomen being as a rule much shorter than that of closely allied genera. 

 The labium is broad at the proximal end of the median lobe and the 

 median process of the proximal palpal segment consists of a simple 

 hook similar to the mesal hook of the same segment. The gills are broad 

 and oval to elliptical in outline, are heavily pigmented, and the legs 

 are long and slender, with a number of dark brown rings on the fem- 

 ora and tibiae. The body is dark in color for the most part, and the 

 species live either in the mud on the bottom of sluggish streams or 

 under rocks or debris in the swifter currents. 



The adults are distinguishable from other genera by the dorsal 

 carinae of the femora and the long setae of the front tibiae ; by the 

 point of origin of vein Mo, which is alw^ays beyond the fifth postnodal 

 cross-vein, and by the number of postnodal cross-veins of the front 

 wing, the latter ranging from twelve to seventeen in number. The 

 parameres of the ninth sternum of the male extend caudad to the apex 

 of the segment, and the sternites at the base of the cephalic pair of 

 gonapophyses are distinct and subtriangular. 



Key to Species 



NYMPHS 



a. Labial palpi with a single weak seta on the proximal segment ; gills 

 broad at the tip (Fig. 58), the margins parallel for a considerable 

 distance, and without light cross-bands and not coarsely spotted 



with dark pigment moesta putrida. 



aa. Labial palpi with two or more setae on the proximal segment ; gills 

 tapering to a point, the margins not parallel or parallel for only a 



