Subfamily CorDULINAE 
Strong-flying dragonflies of large size and often of brilliant metallic 
coloration. Eyes very large and broadly attingent, with an angulation 
or low tubercle on their hind margin at the side of the head. Sectors of 
the arculus separate at their origin. Triangle of hind wings retracted 
to the arculus. Anal loop somewhat foot-shaped (in ours), with well 
developed bisector, but with little development of the “‘toe.”’ Males 
with auricles on the sides of the second abdominal segment, and corre- 
sponding notches in the inner margin of the hind wings. 
The nymphs are sprawlers upon the bottom. They are generally 
hairy, dark colored, and stout bodied, and the dorsal hooks when de- 
veloped are rather heavy and not spinelike. 
Our genera have a predominantly northward distribution. They may 
be separated as follows: 
KEY TO THE GENERA 
Adults 
1 Fore wing, veins M, and Cu, divergent to wing margin........ 2. 
Fore wing, veins M, and Cu; convergent to wing margin....... 4, 
2 Fore wing triangle equilateral. Size large (expanse 75)........ 3. 
Fore wing triangle long and narrow. Small size (expanse 46).... 
ts clin te phe peas er nite Piece Praeee he Se Williamsonia, p. 199 
3  Ante- and post-nodal cross veins all blotched with brown...... 
Heth Ps Wise d one Was Sethe eke Ramin aan Be Platycordulia, p. 172 
Only basal ante-nodal cross veins blotched with brown........ 
Pde Nae Ce REE eet SOND PT Oe eet F Neurocordulia, p. 173 
4 Wings with nodal and apical spots........... Epicordulia, p. 175 
Wings with only basal spots or with none..................--. 5. 
5 Basal brown spots large; basal ante-nodal cross veins spotted with 
brown exeept in (Petragoncuria stella)... se 6 oll aloe 6. 
Basal brown spots small or wanting; basal ante-nodal cross veins 
HOU SpOLbed wily DOWIE as sic sats eo lei ee Wee ole ol eee ie 
6 Hind wing with 6 ante-nodal cross veins... .Helocordulia, p. 181 
Hind wing with 4 to 5 ante-nodal cross veins.......:......... 
Ea SRN Tale et Pou) eR ety he ATR Re fealty Tetragoneuria, p. 178 
7 Hind wing with two cubito-anal cross veins. .Somatochlora, p. 183 
Hind wing with one cubito-anal cross veins.................. 8. 
171 
