AQUATIC INSECTS IN THE ADIRONDACKS 463 



The nymphs are known for a larger proportion of the genera than in 

 any other subfamily. They are climbers among green plants, over tim- 

 bers, on swaying roots, etc., preferring the border of open water or the 

 edge of a current. They are slender, active, clean, with smooth bodies 

 marked with a color pattern of greens and browns, well adapted to con- 

 cealment in the midst of their natural environment. They will eat al- 

 most any living animal that they can capture and hold, and they eat 

 one another with evident relish. 



The nymphs agree in the possession of the following characters : Head 

 depressed; antennae (when grown) six to seven-jointed, filiform ; eyes 

 large, very prominent, covering the anterolateral angles of the head ; 

 labium very long, reaching between the bases of the middle legs, men- 

 tum flat, not covering the face, median lobe with a minute median cleft, 

 lateral lobe denticulate on inner side, and with a terminal hook, as well 

 as the usual movable hook ; legs slender, fitted for climbing and chng- 

 ing; tarsi three-jointed; prothorax with a transverse, dorsal, flattened 

 area, and a pair of conic processes above each coxa; spiracles large, 

 conspicuous ; abdomen somewhat spindle-shaped, with lateral margins 

 becoming acute posteriorly; lateral spines present on a variable number 

 of the segments ; inferior abdominal appendages at least twice as long 

 as the lateral appendages. -: '*• 



The following tables will enable any one to distinguish the members 

 of our few genera. 



KEY TO GENERA 



ros 



a The radial sector (Es., fig. 9) simple 



& But two cubito-anal cross veins; vein M2 undulate; supratriangle with- 

 out cross veins ; but one cross vein under the stigma . .Gomphaeschna 

 hh With three or more cubito-anal cross veins ; vein M2 not undulate ; supra- 

 triangle divided by cross veins ; several cross veins under the stigma 



c Basal space traversed by cross veins Boyeria 



cc Basal space open , Basiaeschna 



aa Radial sector bearing an apical fork 

 h Sectors of the arculus (veins M1-3 and M4 ) separating from the arculus at or 

 below its middle 



c The radial sector symmetrically forked, between it and the supplementary 



vein below it, one or two rows of cells 



d Face strongly produced above, the upper margin of the frons very acute ; 



the veins Mi and M2 parallel to the level of the stigma ; radial sector 



and the supplementary vein below it separated by a single row of cells 



Na siaeschua 

 dd Face vertical, not sharply angulate at upper edge of frons ; veins Mi 

 and M2 approximated at the stigma ; the radial sector and the supple- 

 mentary vein below it separated by two rows of cells 



Epiaeschua 



cc The radial sector strongly deflected toward the stigma at the base of its 



fork, unsymmetric; between it and the supplementary vein below it, 



three to seven rows of cells Aeschna 



hh Sectors of the arculus springing from above the middle of the arculus. An ax 



