AQUATIC INSECTS IN THE ADIRONDACKS 44/ 



Nymph. Abdomen a little wider than the head, the ninth segment 

 hardly longer than the eighth; lateral spines on segments 6-9, a well 

 marked middorsal impressed line extending to the eighth segment, and 

 very minute rudiments of dorsal hooks on segments 8 and 9 ; tibial bur- 

 rowing hooks large; front border of median lobe of labium straight, 

 lateral lobe with its terminal hook bent inward at almost or quite a right 

 angle ; apex of abdomen regularly narrowed beyond the middle. 



KEY 



a) Imago Face entirely yellow; nymph unknown 1. G. ventricosus 



aa) Imago Face with narrow black lines on sutures ; sides of hind femora 



yellow; nymph unknown G. amnio ola 



aaa) Imago Face with broad transverse bands of black ; Mud femora black ; 

 abdominal segments with basal rings of yellow; nymph with the lateral 

 spines of the ninth segment less than half as long as the 10th segment 



G. scudderi 



aaaa) Imago Face with broad transverse bands of black ; hind femora black; 



yellow of middle abdominal segments restricted to triangular spots on 



the dorsum; nymph with the lateral spines of the ninth segment about 



as long as the 10th segment G. vastus 



Subgenus stylurus 



Imago. A single cell between veins Ai and A2 at their origin, that cell 

 strongly bordered ; abdominal segments 7-9 not greatly dilated (much 

 narrower than the thorax), but considerably elongated ; eighth segment 

 cut squarely at apex; posterior genital hamule of male strongly directed 

 anteriorly; hind femora similar in the two sexes. 



Nymph. Abdomen narrower than the head, and greatly elongated; 

 tibial burrowing hooks very small ; lateral spines, middorsal suture and 

 dorsal hooks of abdomen as in Gomphurus; ninth abdominal seg- 

 ment longer than the eighth, sometimes twice as long. 



KEY 



d) Imago. Ninth abdominal segment of imago much shorter than the 

 seventh. Nymph with the lateral spines of the ninth abdominal seg- 

 ment longer by half than the 10th segment G. plagiatus 



aa) Imago with segments 7 and 9 of abdomen about equal in length. Nymph 

 with the lateral spines of the ninth abdominal segment shorter by half 

 than the 10th segment G. spiniceps 



Subgenus arigomphus 



Imago. Two cells between the base of veins Ai and Ao at their origin ; 

 eighth abdominal segment obliquely cut at apex, longer on the dorsal 

 side ; hind femora different in the two sexes, in the male hairy, and in 



