AQUATIC INSECTS IN THE ADIRONDACKS 435 



flowing or clear water; abundantly represented throughout New York 

 state. The nymphs are burrowers in the beds of streams and ponds. 

 The females oviposit unattended by the males, and liberate their eggs in 

 the water during flight by descending repeatedly and striking the surface 

 of the water with the tip of the abdomen. The eggs have a scanty 

 envelop of gelatin; they tend apart in falling, to lie scattered on the 

 bottom, where they are at once hidden by the silt which adheres to the 

 gelatin. The following key will serve for the separation of the genera 

 likely to be found within our limits. 



KEY TO GENERA 



Iinagos 

 a Basal subcostal cross vein («ee fig. 9) present; a linear or spatalate, 

 median, sternal process on the first abdominal segment ; legs very short, 

 the hind femora hardly reaching the apex of the first abdominal seg- 

 ment Progomphus 



aa No basal subcostal cross vein ; no median sternal process on the first 

 abdominal segment; legs longer, the hind femora reaching or surpassing 

 the middle of the second abdominal segment 

 & Hind wings with a distinct anal loop (see fig. 18 a) consisting of several 

 cells 

 c Anal loop normally consistingof three cells ; first and fifth antenodal cross 

 veins matched in position and bypertrophied ; stigma broad with both 

 sides convex; triangles not traversed by cross veins. O phiogomphus 

 cc Anal loop consisting normally of four cells; first and seventh antenodel 

 cross veins matched in position and bypertrophied; stigma long and 

 narrow with parallel sides; each triangle divided by a cross vein 



H ageni u s p. 440 



&& Hind wings with no distinct anal loop, or with one consisting of a single cell 



c Triangle of the fore wing one third shorter than that of the hind wing; 



generally a single cell between the bases of veins A2 and A3 . . L a n t h u s 



CG Triangle of the fore wing less tlian one fourth shorter than that of the 



hiud wing ; generally, two or more cells between A2 and A3 at their origin 



d Hind femora naked, or with numerous short spines 



G o m p h u s , sens. lat. p. 443 

 dd Hind femora with five to seven long, strong spines 



D r o m o g m p h u 8 p. 461 

 Nymphs 



a Middle legs more approximate at the base than are the fore legs; fourth seg- 

 ment of the antenna slender, erect, about as long as the third segment is 

 wide ; 10th abdominal segment about as long as the ninth 



Progomphus 



aa Middle legs not more (usually less) approximate than the fore legs at base; 



the fourth segment of the antenna a mere rudiment, orbicular or discoid, 



much shorter than the third segment is wide; 10th abdominal segment 



much shorter thau the ninth 



