92 DRAGONFLIES OF OHIO. 



The members of this sub-family are medium sized to 

 large species with ample wings and short, thick bodies. 

 In some species males and females are colored differently, 

 while in others both sexes are alike. Most of the forms 

 are easily collected on account of their abundance, but 

 there are a few species that occur over large areas and 

 are never common anywhere, these are usually procured 

 with difficulty. The Ohio species are placed in ten 

 genera which may be separated by the following table : 



1. Hind wings very wide at base, fore wings, except in some cases 

 at extreme base, entirely transparent 3 



2. Hind wings not extremely wide at base 4 



3. Base of hind wing black or brown for its entire width Tramea 



Base of hind wing transparent with anal margin yellowish, or 

 infuscated at anal angle... Pantala. 



4. Hind lobe of the prothorax large, bilobed 5 



Hind lobe of the prothorax small, entire 10 



5. Sectors of the arculus pedicellate 6 



Sectors of the arculus not pedicellate 9 



6. Both sectors of the triangle in the hind wings arising from its 



hind angle , 7 



Lower sectors of the triangle in the hind wings arising from its 

 hind angle, the upper from its outer side 8 



7. Nearly black species, extreme base of hind wings black, front 



white Leucorhinia. 



Never black, extreme base, sometimes basal half, of hind wings 

 yellowish brown, front variously colored but never pure white, 



Diplax. 



8. Base of hind wings perfectly transparent, thorax unicolorous, 

 last antecubital of 'front wings usually not continued to median 



vein Mesothemis. 



Base of hind wings yellowish brown, thorax banded with black 

 and olive, last antecubital of front wings usually continued to 

 median vein Pachydiplax. 



9. Small species, expanse about 30 millimeters, hamule of male not 



bifid Perithemis. 



Larger species, hamule of male bifid Celithetnis. 



10. Male with a pair of ventral hooks on first abdominal segment, 



third tibiae, as long as third femora Plathemis. 



Male with no ventral hooks, female with third tibia; at least a 

 little longer than third femora Libellula. 



