AQUATIC INSECTS 



9 2 3 



4 (3) Basal space of all wings traversed by cross veins Hetaerina. 



5 (2) Quadrangle without cross veins; antenodal cross veins but two in each 



wing; pterostigma with a brace vein at its proximal end in 

 the space behind vein RI; wings narrower. ..... 6 



6 (9) Vein M 3 arising (i.e., separating from vein Mi+ 2 ) nearer the arculus 



than the nodus 7 



r, (IM LJLI i 1 i 1 I 'l I I I I 'i ' i' rLjrV- 



FIG. 1388. Wing venation in the Odonata: (a) a dragonfly, Cordulegaster. (V) a damselfly, Argia; 

 (c) the region of the stigma, st, with its brace vein, z, ar, arculus; al, anal loop; br, bridge; n, nodus; 

 o, oblique vein; /, triangle; /', subtriangle; q, quadrangle; sq, subquadrangle; v, basal subcostal cross 

 veins; z, veins as in Fig. 1386. 



7 (8) Vein M 2 separating from vein MI at a distance of several cells beyond 



the subnodal cross vein. Lestes. 



8 (7) Vein M 2 separating from vein M! close to the subnodal cross vein, less 



than the distance of one cell beyond it. . Archilestes. 



9 (6) Vein M 3 arising nearer the nodus than the arculus 10 



10 (n) Spines on the tibiae very long, twice as long as the intervals between 



them Argia. 



1 1 (10) Spines of the tibiae hardly longer than the intervals between them. 1 2 



12 (16) No pale postocular spots on the top of the head; sexes similarly 



colored 13 



13 (14, 15) Colors of dorsum blue and black; yellow beneath the thorax. 



Chromagrion. 



14 (13, 15) Colors of dorsum red and black; stout species. . Amphiagrion. 



15 (13, 14) Dorsum bronzy green; slender species. . . . Nehallennia. 

 16(12) With round or ovoid postocular spots on the head 17 



17 (18) Sexes with a general similarity in color, the female often of a lighter 

 shade; the superior abdominal appendages of the male 

 not strongly directed downward and inward. . . Enallagma. 



