AQUATIC INSECTS IN THE ADIRONDACKS 53I 



known, and are described and distinguished below. So much ahke are 

 they that a general account of the nymphal characters will save much 

 restatement. 



The known nymphs of this genus agree in having the body elongate, 

 tapering to the pointed apex of the abdomen, hairy, the hairs serving to 

 hold an ambuscade of silt about the body. Plead compact, httle wider than 

 long, with the eyes capping the anterolateral angles, and directed ante- 

 riorly; head little narrowed behind the eyes; labium large, reaching 

 posteriorly between the bases of the middle legs ; median lobe with its 

 front border not crenate; mental setae always present, variable in 

 number ; lateral setae five to nine ; prothorax with a flatish dorsal shield, 

 whose margins are generally fringed with coarse hairs ; wing cases reach- 

 ing the base of the sixth abdominal segment; abdomen triquetral, 

 its lateral margins becoming acute posteriorly, with short lateral spines 

 on segments 8 and 9 ; a variable number of dorsal hooks beginning 

 on the third or fourth segment, sometimes quite rudimentary ; ninth 

 segment two to three times as long as the loth ; lateral appendages half 

 as long as the others; tarsi with the second and third joints successively 

 each a very little longer than the first. 



The imagos discussed below, and the known nymphs of the same 

 species may be separated by the following keys. 



KEY TO SPECIES OF LIBELLULA 



Imagos 



a Wings with no spot at the nodus 



6 "With a broad basal band of black covering the basal third of both wings 



bas al is 



&& With the black color of the base of the wings confined to a narrow streak 



in the subcostal space, or entirely wanting 



c Stigma bicolored 



d Inner half of stigma white or yellow, outer half dark brown, c y a n e a 



dd Stigma mainly yellow, but distinctly darker at the outer end 



p 1 u m b e a 

 CO Stigma not differing in color at its inner and outer ends 



d Stigma red or yellow; wings flavescent, unspotted auripenuis 



dd Stigma black iucesta 



aa Wings with a small nodal spot which is restricted to the outer (distal) 

 side of the nodus 

 J With a large triangular patch of black extending from the triangle to the 



hind margin quadriraac ulata 



5& Without a black patch between the triaugle and the hind margin in the 



hind wing vibrans 



aaa With a large nodal spot which completely surrounds the nodus 



& Nodal and apical wing spots yellowish or reddish semifasciata 



&& Nodal and apical wing spots blackish pulchella 



