AQUATIC INSECTS IN NEW YORK STAI 



231 



tions of imagos. I present a key based chiefly on the form of the 

 male appendages, which will be sufficient, I trust, for the deter- 

 mination of species. Of these nine species I have reared five, 

 I regret to acknowledge, after prolonged study of them, that I 

 find them well nigh indistinguishable specifically. Aside from 

 slight and inconstant differences in size and a few very minor 

 structural characters, they are all alike. I will give therefore a 

 general description of them and supplement it with a tabular 

 statement of such differences as I have thus far been able to 

 discover between them. 



Nymph. The nymph of Lestes is exceedingly long and 

 slender, with wide head, deep thorax and slender, cylindiic ab- 



Fig. 7 Nymph of Lestes rectangular is; A, gills, more enlarged 



domen, bearing linear-oblong gill plates. Head twice as wide 

 as long, only moderately prominent at the front; eyes prominent, 

 rounded, directed somewhat anteriorly; hind angles low, well 

 rounded, with a shallow wide notch between them on the hind 

 margin; antennae longer than the head, with the segments in- 

 creasing in length to the third, and decreasing thereafter to the 

 tip, seven-jointed. Labium [i)1.14, fig.c] long and exceedingly 

 slender, the hinge reaching as far posteriorly as the hind legs, 

 but dependent, and not closely applied to the ventral surface of 

 the body; mentum linear to the suddenly dilated, and spoon- 

 shaped tip; median lobe moderately prominent, with a closed 

 median cleft which extends as far proximally as the level of the 

 bases of the lateral lobes; mental setae well developed; lateral 

 lobe very complicated [see pi. 14, fig.cZ], bent almost at a right 

 angle just beyond its base, having a very large movable hook, be- 

 yond the base of which the distal portion is cleft into two parts, 

 the inner one of which bears the end hook and the usual inner 

 series of teeth, these being very numerous, regular and deeply 

 cut; the outer part is widened distally, with its distal angles pro- 



