ODONATA. 
Ins. 207 
B. Inferior sector of the triangle originating at the basal 
post-costal nervule, or somewhat before in the 
anterior. Pterostigma similar in the four wings. 
A. No post-ocular spots Oxyagrion 
(subg. n.), p. 46. 
B. With post-ocular spots Acanthagrion 
(subg. n.), p. 60. 
Section 2. — The 10th segment of the $ not elevated. 
A. Inferior sector of the triangle originating at the basal 
post-costal nervule. No post-ocular spots . . Xiphiagrion 
(subg.n.),p.77. 
B. Inferior sector of the triangle originating before the 
, basal post-costal nervule. With post-ocular spots . Enallagma 
(subg. n.), p. 79. 
II. — No spine at the apex of the 8th segment of the $ , beneath. 
Section 1.— Inferior sector of the triangle originating before the basal 
post-costal nervule. (Sub-genera inhabiting especially the 
boreal hemisphere.) 
A. With pale post-ocular spots. 
a. Abdomen extremely slender, its markings 
nearly similar in both sexes ; coloration 
metallic green Nehalennia. 
b. Abdomen less slender, its markings diifering in 
the sexes ; coloration less metallic. . . Agrion. 
B. No post-ocular spots. 
a. Coloration red ....... Pyrrhosoma. 
b. Coloration bronzy on a blue or yellowish ground Erythromma. 
Section 2. — Inferior sector of the triangle originating at the basal 
post-costal nervule, or scarcely before. 
§ Sub-genera of the Old W orld. 
A. With pale post-ocular spots. Abdomen slender or 
moderate, the markings differing in the sexes. 
a. Prothorax of the $ furnished with two pro- 
cesses directed backward .... Pseudagrion 
(subg. n.), p. 200. 
b. Prothorax of the $ simple .... Xanthagrion 
(subg. n.), p. 230. 
B. No post-ocular spots. Abdomen moderate, the mark- 
ings nearly similar in the sexes. 
a. Coloration yellow or reddish; spines of the 
tibiae moderate ...... Ceriagrion 
(subg. n.), p. 235. 
b. Coloration green and black ; spines of the 
tibiae long, widely divergent ( $ unknown) . A rgiagrion 
(subg. n.), p. 240. 
