AQUATIC INSECTS IN THE ADIRONDACKS 



479 



long, reaching the sixth abdominal segment when the nymph is grown ; 

 lateral spines are present on abdominal segments 8 and 9, but the dorsal 

 hooks are very variable, and often wanting. 



Of the three subfamiHes characterized below, the first one is here 

 newly set apart; the other two are so closely aUied that no single abso- 



Fig. 18 Bases of wings of Leucorhinia glacialis Hagen. Ccosta; 5c subcosta ; i2 radius; 

 Jf media; Cw cubitus; A anal vein; ararculus; t triangle; i' subtriangle ; s supra triangle; a anal 

 loop 



lutely distinctive character has yet been found that will separate all the 

 imagos. A combination of characters seems to be necessary for dis- 

 tinguishing both imagos and nymphs: a combination is therefore used in 

 the following tables. 



KEY TO SUBFAMILIES 



Imagos 

 a The triangle of the hind wing placed considerably beyond the arciilns ; the 

 anal loop well developed, and hardly longer than broad; with more than 



two cubito-anal cross veius ., Macromiinao 



aa The triangle of the hind wing (fig. 18) retracted to the level of the areulus 

 or even passing it a little sometimes; the anal loop, greatly elon"-ated 

 (except in Nannothemis) and becoming foot-shaped : one or two 

 cubito-anal cross veins. 



