472 CALIFORNIA ACADEMY OF SCIENCES. 



c. Sectors of the arculus in the frout wings arising by a dis- 

 tinctly common stalk; triangle of hind wings free. (Triangle 

 of frout wings not broken to form a trapezium.) 



Last antenodal on front wings continued to the median vein; 

 inner side of triangle of hind wings in the prolongation of 

 the arculus. 



Nodal sector distinctly waved in its middle, frons with- 

 out lateral vertical carinai as in Orthetrum, vertex con- 

 cave at tip, no feupratriangulars, abdomen stout. 



Orthemis. 

 Last antenodal on front wings not continued to the median 

 vein. 



Sectors of the triangle in the hind wings arising from the 

 hind angle. 

 Nodal sector waved in its middle, inner side of the 

 triangle of hind wings in the pi-olongation of the 

 arculus, triangle of front wings cross-veined. 



Dythemis. 

 Nodal sector not waved in its middle, no supratrian- 

 gulars, no additional carina on 4th ab. seg. 



Triangle of front wings free, tooth of tarsal nails 

 as long as tip of nail itself (except in M. ine- 

 quiunguis) . Macrothemis. 



Triangle of front wings cross-veined except fre- 

 quently in T. minuscida Kamb., tooth of tarsal 

 nails much shorter than tip of nail itself. 



Trithernis. 

 Sectors of the triangle in the hind wing arising, the lower 

 from the hind angle, the upper from the outer side. 



Mkrathyria. 

 B. Hind lobe of the prothorax erect, wider than the other lobes, its 

 hind margin usually bilobed. 



Sectors of the triangle in the hind wings arising from its hind 

 angle. 



Hamule of male bifid. Nodal sector not waved, last ante- 

 cubital on frout wings rarely continued to median vein, 

 vertex truncated, abdomen and hind wings without the char- 

 acteristic color patterns of Celithemis and Leucorhinia. 



DijAax. 



Hamule of male not bitid. No additional transverse carina 



on 4th ab. seg. Caniiacria. 



Sectors of the triangle in the hind wings arising, the lower from 



its hind angle, the upper from its outer side; the front wings 



with the sectors of the arculus arising by a common stalk, and 



