1. Abdomen with middorsal hook, spine, or knowb on at least segments 6 or 7 . . . . . . . 2
Abdomen without middorsal hook, spine, or knob on segments 6 and 7. . . . . . . . . . 14
2. A middorsal hook, spine, or knob on abdominal segment 9. . . . . . . . . . . . . . . . .. . . . 3
No middorsal hook, spine, or knob on abdominal segment 9. . . . . . . . . . . . . . . . . . . . 8
3. Lateral spines of abdominal segment 9 reaching to tip of epiproct or beyond. . . . . . . . 5
Lateral spines of abdominal segment 9 not reaching beyond middle of epiproct . . . . . . 4
4. Each cercus about as long as epiproct; 6-8 palpal setae. Corduliidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Somatochlora (in part)
Each cercus about half as long as epiproct; 5 palpal setae. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Perithemis tenera
5. Middorsal hooks knob-like, with ends blunt and rounded; each indentation on palpal lobes 2 or more times as deep as wide. Corduliidae. . . . . . . . . . . . Neuroocordulia
Middorsal hooks spine-like, ending in a sharp point; each indentation on palpal lobes at most as deep as wide. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Middorsal hooks absent on abdominal segments 1-5 or 1-6. Corduliidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Helocordulia uhleri
Middorsal hooks present on abdominal segments 2-9 or 3-9. . . . . . . . . . . . . . . . . . . . 7
7. Outer half of dorsal surface of prementum thickly covered with setae; palpal setae usually 4, rarely 5. Corduliidae. . . . . . . . . . . . . . . . .Epitheca (subgenus Epicordulia)
Outer half of dorsal surface of prementum with few very small setae; papal setae usually 6-7, rarely 8. Corduliidae. . . . . . . . . . . . . . . . . . .Epitheca (subgenus Tetragoneuria)
8. Each cercus 2/3 to equal the length of paraprocts. Corduliidae. . . Dorocordulia libera
Each cercus less than 2/3 length of paraprocts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. Premental setae 0-3, all fine or inconspicuous. Libellulidae. . . . . . . . . . . . . . . Ladona
Premental setae 7-21, all prominent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Lateral spines of abdominal segment 9 long and straight, reaching to or beyoond tips of paraprocts and about twice middorsal length of segment 9. Libellulidae. . . Celithemis
Lateral spines of abdominal segment 9 lass than twice middorsal length of segment. . 11
11. Eyes situatied on the front corners of the head so that their length is distinctly less than the lateral distance behind the eyes; body with numerous long hairs. . . . . . . . . . . . . 12
Eyes more lateral so that their length is greater than or equal to the lateral distance behind the eyes; body with only scattered long hairs. . . . . . . . . . . . . . . . . . . . . . . . 13
12. Abdominal segments 7-9 with brown or black, shining middorsal ridge; ligula margin finely notched. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plathemis lydia
Abdominal segment 7-9 without dark middorsal ridge; ligula evenly coontoured, without shallow notches. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Libellula (in part)
13. Middorsal hook present on segment 3 (count from 9th segment forward); epiproct and paraprocts about equal in length; dark marking usually present on bottom of abdominal segments. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Leucorrhhinia (in part)
Middorsal hook absent on segment 3 (count from 9th segment forward); epiproct usually noticably shorter than paraprocts; no dark markings on bottom of abdominal segments. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sympetrum (in part)
14. Outer third of cerci and paraprocts strongly curved downward; no lateral spines on abdomen; palpal setae 7-9. Libellulidae. . . . . . . . . . . . . . . . Erythemis simplicicollis
Outer third of cerci and paraprocts straight; lateral spines may or may not be present on abdomen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
15. Lateral spines prominent on abdominal segment 8, at least as long as middorsal length of that segment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Lateral spines on abdominal segmetn 8 absent, or smaller than the middorsal length of that segment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
16. Crenations* of palpal lobes deep; epiproct as long as or longer than paraprocts. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pantala
Crenations* of palpal lobes shallow; epiproct shorter than paraprocts. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tramea
17. Tips of lateral spines of abdominal segment 9 extending beyond tip of epiproct. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pachydiplax longipennis
Tips of lateral spines of abdominal segment 9 not extending beyond tip of epiproct. . 18
18. Cerci not more than 1/2 length of paraprocts; if eyes large and on lateral margins of head, then lateral spines on abdomiinal segment 8 at least 1/2 the middorsal length of that segment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Cerci more than 2/3 the lengths of the paraprocts (except Sympetrum, where cerci can be less than 1/2 the length of the paraprocts and eyes are large and on outer margins of head, but lateral spines on abdomial segment 8 are less than 1/3 middorsal length of that segment). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
19. Eyes small and on front outer corners of head; laateral spines of abdomiinal segments 8 and 9 nearly equal in length; body very hairy; bottom of abdomen without dark markings. Libellulidae. . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . Libellula (in part)
Head with eyes larger and more laterally located; lateral spines of abdodminal segment 9 longer than those of segment 8; body either less hairy or smooth; dark markings on bottom of abdomen. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . Leucorrhina (in part)
20. Abdominal segments 4-9 with middorsal humps on middle of back bearing a tuft of thick hairs. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Erythroddiplax
Abdominal segment bumps not bearing tufts of hairs. . . . . . . . . . . . . . . . . . . . . . . . 21
21. Paraprocts nearly equal in length to epiproct; mature larva small, less than 11 mm; six palpal setae. Libellulidae. . . . . . . . . . . . . . . . . . . . .. . . . . . . . . Nannothemis bella
Paraprocts longer than epiproct; larva larger, >12 mm; seven to 16 palpal setae. . . . . 22
22. A dark longitudinal stripe present along the upper lateral margin of the thorax; palpal setae 7; indentations of palpal lobes of intermediate depth. Corduliidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cordulia shurtleffii
No dark stripe present on thorax; usually more than 7 palpal setae (may be 7 in Somatochlora, then indentations deep); indentations of palpal lobes either very deep or very shallow, not intermediate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
23. Indentations of palpal lobes sallow, cerci 2/3 length of epiproct or slightly less; palpal setae 9 or more. Libellulidae. . . . . . . . . . . . . . . . . . . . . . . . . . Sympetrum (in part)
Indentations of palpal lobes deep; cerci nearly equal to length of epiproct; palpal setae 7-8. Corduliidae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Somatochlora (in part)
*Crenations are the small, evely rounded (not deeply curved) scallops or notches that are on the outer edges of the palpal lobes.
