1. Outer margin of palpal lobes produced into 3 pointed hooks; premental setae absent; body usually short and stout. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Argia
Outer margin of palpal lobes with a small end hook and a more or less truncate and toothed middle lobe; premental setae present; body usualy longer and more slender. . . . . . . . . . . . . 2
2. Rear outer margins of head angulate, with angles projecting and forming blunt tubercles. . . . . 3
Rear out margins of head broadly rounded, without blunt tubercles. . . . . . . . . . . . . . . . . . . . 4
3. Antennae 5- or 6-segmented; caiudal lamellae about 1/3 as broad as long, margins thickly set with setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Amphiagrion saucium
Antennae 7-segmented; caudal lamelae aboutr 1/6 as broad as long, margins with widely separated setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chromagrion conditum
4. Prementum with 1 or 2 dorsal setae on each side of median line, the second, when present, very small. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nehalennia
Prementum with 2 to 7 well-developed dorsal setae on each side of median line. . . . . . . . . . 5
5. Antennae 6-segmented. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Enallagma
Antennae 7-segmented. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Caudal lamellae terminating in a blunt point. . . . . . . . . . . . . . . . . . . . . . . . . . . . Coenagrion
Caudal lamellae terminating in a sharp tapered point. . . . . . . . . . . . . . . . . . . . . . Ischnura
