124 



Smith and Pritchard: Odonata 



the present rules of zoological nomenclature. This 

 interpretation would make Triacanthagyna a synonym 

 of Gynacantha, and Gynacantha, in the sense of 

 having biacanthagyne characteristics, would be re- 

 placed by Acanthogyna Kirby 1890 (with the type 

 Gynacantha nervosa by designation of Cowley, 1934). 

 However, we propose to use the well-established 

 interpretations of these genera rather than make such 

 a confusing switch. 



Family LIBELLULIDAE 



The members of the family Libellulidae are mostly 

 showy dragonflies commonly seen hovering over the 

 surface of still water. They vary greatly in size; in 

 our fauna the smallest is about an inch in length, 

 and the largest about four inches. The bodies of 

 these dragonflies are in general stouter and less 

 elongated than the Aeshnidae and Gomphidae. 



The females do not possess a well-developed 

 ovipositor but merely drop their eggs into the water 

 or place them about plants at the surface of the water. 



The naiads are usually protectively colored and 

 sprawl on the bottom in shallow water or clamber 

 over fallen plant debris. They possess a characteristic 

 spoon-shaped, masklike labium. 



Many authors split this group into two or three 

 parts, each of family rank. Because of difficulties 

 involved in characterizing the naiads at the family 

 level, they are considered here as subfamilies. 



Key to Nearctic Genera 

 Adults 



1. Anal loop much longer than wide, its cells divided into 

 2 rows; hind wing with triangle close to arculus (fig. 

 4:40) 2 



— Anal loop little longer than wide, its cells not arranged 

 in 2 rows; hind wing with triangle remote from arculus 

 (fig. 4:35) MACROMIINAE 3 



2. Anal loop not boot-shaped, distal angles similarly 

 developed (figs. 4:37; 4:38; 4:39); posterior margin of 

 eye emarginate; male with auricles on second abdominal 

 segment and with anal lobe of hind wing notched . . . 



CORDULIINAE 4 



— Anal loop boot-shaped, the toe rarely absent; posterior 

 margin of eye rounded (fig. 4:40); male without auricles 

 on second abdominal segment and with anal lobe of 

 hind wing smooth LIBELLULINAE 11 



3. Occiput larger than vertex; space above bridge with 4 to 

 6 cross veins Didymops Rambur 



— Occiput smaller than vertex; space above bridge with 

 2 or 3 cross veins (fig. 4:35) Macromia Rambur 



4. Fore wing with M 4 and Cu, divergent 5 



— Fore wing with M 4 and Cu, convergent (fig. 4:37) ... 6 



5. Fore wing with triangle equilateral 



Neurocordulia Selys 



— Fore wing with triangle long and narrow 



Williams onia Davis 



6. Wing with large maculations at the base, nodus, and 

 distal end Epicordulia Selys 



— Wing without distal marking and without a separate 

 nodal maculation 7 



7. Hind wing with 2 cubito-anal cross veins; bisector of 

 anal loop closer to A 2 than to A,; wings without fuscous 

 spots (fig. 4:37) Somatochlora Selys 



— Hind wing with 1 cubito-anal cross vein; bisector of 



10. 



11. 



12. 

 13. 



14. 

 15. 



16. 



17. 



18. 



19. 



20. 



21. 



22. 



23. 



24. 

 25. 



26. 



27. 



28. 



anal loop equidistant from A, and A 2 (fig. 4:38)) .... 8 

 Fore wing with triangle open . . . Dorocordulia Needham 

 Fore wing with triangle having a cross vein (figs. 4:38; 



4:39) 9 



Hind wing with proximal infuscation (except in one 



species from Florida) 10 



Hind wing without infuscation (northern U.S., Canada) 



(fig. 4:38) Cordulia Leach 



Hind wing with 6 antenodal cross veins 



Helocordulia Needham 



Hind wing with 4 or 5 antenodal cross veins (fig. 4:39) 



Tetragoneuria Hagen 



Stigma with ends parallel (figs. 4:43; 4:45) 12 



Stigma trapezoidal (figs. 4:41; 4:55; 4:57) 33 



Anal loop complete, more or less foot-shaped 13 



Anal loop open at wing margin .... Nannothemis Brauer 

 Pronotum with caudal lobe erect, as wide as pronotum 



and bilobulate 14 



Pronotum with caudal lobe directed caudad, narrower 



than the pronotum and usually entire 23 



Bisector of anal loop nearly straight 15 



Bisector of anal loop distinctly angulate beyond middle 



(fig. 4:44) 16 



Fore wing with triangle as broad as long 



Perithemis Hagen 



Fore wing with triangle longer than broad 



Celithemis Hagen 



Hind wing with Cu, arising from outer face of triangle 



(fig. 4:40) 17 



Hind wing with Cu, arising from posterior angle of 



triangle (fig. 4:48) 20 



Fore wing with distal antenodal matched (fig. 4:53) 

 18 



Fore wing with distal antenodal unmatched (fig. 4:52) 



19 



Wing with 2 or more cross veins under stigma 



Leucorrhinia Brittinger 



Wing with only 1 cross vein under stigma 



Pachydiplax Brauer 



Radial planate subtending 1 row of cells (fig. 4:52); 



tibial spines about as long as intervals 



Erythemis Hagen 



Radial planate subtending 2 rows of cells, tibial spines 



much longer than intervals Lepthemis Hagen 



Wing with 2 or more cross veins under stigma 21 



Wing with not more than 1 cross vein under stigma 



(figs. 4:48; 4:51) 22 



Median planate subtending 2 rows of cells; hind wing 



with 7 or 8 antenodal cross veins 



Cannacria Kirby 



Median planate subtending 1 row of cells; hind wing 

 with 6 antenodal cross veins 



Brachymesia Kirby 



Abdomen with a transverse carina on 4th segment 



Tametrum Needham and Fisher 



Abdomen without a transverse carina on 4th segment 



Sympetrum Newman 



Hind wing narrow at base, with 2 cubito-anal cross 

 veins, and with vein Cu, arising from outer side of 



triangle (Texas and West Indies) Cannaphila Kirby 



Hind wing wider at base; veins not as above 24 



Fore wing with distal antenodal matched 25 



Fore wing with distal antenodal unmatched (fig. 4:54) 



30 



Hind wing with Cu. arising from hind angle of triangle 



26 



Hind wing with Cu, arising from outer face of triangle 



Erythrodivlax Brauer 



Wing with 1 bridge cross vein (fig. 4:43) 



Orthemis Hagen 



Wing with 2 or more bridge cross veins (fig. 4:44) 



26 



Fore wing triangle with 3 or more cells (fig. 4:44; 4:45) 



27 



Fore wing triangle with only 2 cells . . Ladona Needham 

 Arculus near middle of distance between first and 

 second antenodal cross vein (fig. 4:45); male with a 



