NO. 1571. DRAGONFLIES OF BURMA AND SIAM— WILLIAMSON. 273 



basal antenodal of second series wanting; sectors less curved, 

 R3 meeting the hind margin of wing at an acute angle . Hagenius «■ 

 hh. Triangle of front wing free; arculus in front and hind wings near 

 the third antenodal; anal area of front wing with 1 row of cells 

 proximal to the triangle, followed by not more than 2 rows; M4 

 and Cui in front wing nearly parallel, about 9 cells between at 

 margin; in hind wing 1 cross vein between Mi_3 and M^; tri- 

 gonal supplement not distinct; distance from forking of Mi_2 

 and M3 to subnodus greater in front wing than in hind 



wing Davidius 



gg. Triangles, subtriangles, and supertriangles all normally free; dis- 

 tance from forking of Mi_2 and M3 to subnodus greater in front wing 

 than in hind wing; sectors uniformly curved ; trigonal supplement 

 not distinctly developed; stigma short, usually one-fourth or less 

 in distance from nodus to distal end of stigma. 

 h. Normally with 3 or more cross veins between M1-3 and M4 in hind 

 wing and 4 or more in front wing; Mj.., and M^ approximated at 

 or immediately beyond their origin at the arculus; stigma with- 

 out brace vein. 

 i. Basal antenodal of second series present in all wings (excepting 

 in Leptogoviphus sp.); anal area of front wing with 1 or 2 rows 

 of cells before the triangle, followed by 2 or more rows. 

 j. More than 2 rows of cells between Mi and Mj^ at level of distal 

 end of sti'gnia; anal area of front wing with maximum width 

 of 3 or more cells; proximal angle of triangle in front wing 

 not as far distant from arculus as length of proximal side of 

 subtriangle; forking of Mi_3 and M4 in hind wing symme- 

 trical Macrogomphus 



jj. One row of cells (rarely 2) between M^,aud AIi_^ at level of distal 

 end of stigma; anal area of front wing with a maximum width 

 of 2 cells; proximal angle of triangle in front wing at least as 

 distant from arculus as length of proximal side of subtriangle; 

 forking of Mi_3 and M^ in hind wing unsymmetrical. 



Leptogoviphus 

 a. Basal antenodal of second series wanting; anal area of front wing 

 with 1 row of cells throughout; 1 row of cells between Mj and 

 Mi,^ at level of distal end of stigma; proximal angle of triangle 

 in front wing at least as distant from arculus as length of prox- 

 imal side of subtriangle; forking of M^_.^ and M^ in hind wing 



unsymmetrical Mierogomphus 



hh. Normally with 1 cross vein (rarely 2) between Mi_3 and M^ in hind 

 wing and 4 or less in front wing; Mi_3 and M^ distinctly separated 

 at ajid beyond their origin at the arculus; forking of Mi_3 and 

 M4 in hind wing symmetrical or not distinctly unsymmetrical; 

 stigma with or without brace vein; proximal angle of triangle in 

 front wing not as distant from arculus as length of inner side of 

 subtriangle. & 



a Characters based on a study of the American H. brevistylus, the only species of the 

 genus known to me. 



b The following genera form a group of great venational uniformity marked by 



many minor diversities. At least 2 of them are of very wide distribution and others, 



not regional and not here considered, find their closest allies here. Genera have 



developed these many minor venational characters independently, at least in many 



Proc. N. M. vol. xxxiii— 07 18 



