2 University of Michigan 



If his Diaphlebia nexans is congeneric with the tvpe species, 

 D. augustipennis, as there is no reason to doubt, then Diaphlebia 

 is the nearest relative of Desmogomphus. Desmogomphus has a 

 much shorter stigma (about one-eighth the wing length, about one- 

 sixth or sHghtly longer in Diaphlebia) ; the anal area of the front 

 wing is only one cell wide (two in Diaphlebia) ; and the hind border 

 of the hind wings is normal (not excavated basally as in Diaph- 

 lebia). 



Other venational characters of Desmogomphus may be briefly 

 summarized: triangles, supratriangles, and sub triangles all free 

 except the triangle of the hind wing, which is once crossed; tri- 

 angles of front and hind wings dissimilar, that of front wing nearly 

 equilateral, with the anterior side very slightly the shortest, that of 

 hind wing with the proximal side much the shortest; sub triangles 

 distinct (i.e., A angled at the proximal angle of the subtriangle) ; 

 M4 and Cux in front wing more widely separated at the level of the 

 nodus than at the triangle; M3 in front wing terminating far proxi- 

 mal to the level of the stigma; cross-veins between Mi_3 and M4 

 numerous and unspecialized ; two rows of post- trigonal cells in the 

 front wing, three, followed immediately by two, in the hind wing; 

 forking of Mi-j and M3 unsymmetrical; basal antenodal of second 

 series wanting; distal thickened antenodal the fifth; anal area of 

 front wing one cell wide, of hind wing three cells wide, the two 

 anterior postanal cells undivided; anal triangle three-celled, not 

 reaching the anal angle; membranule wanting. 



While the affinities of Desmogomphus are, I think, with Pro- 

 gomphus and Gomphoides, there is a striking resemblance between 

 the front wings of Ischnogomphus and Desmogomphus. Ischno- 

 gomphus and Progomphus, for example, belong, I believe, to two 

 lines of descent. By its characters Desmogomphus indicates the 

 common origin of these two lines, and an apparent link between 

 them justifies its name. The relationships will be discussed in the 

 second part of this paper. 



