AQUATIC INSECTS IX NEW YORK STATE 



231 



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

 male appendages, which will be suflScient, 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 yery minor 

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

 general description of them and supplement it with a tabular 

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

 discoyer between them. 



Nymph. The nymph of Lestes is exceedingly long and 

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



Fig-. 7 Ny m|ih of Lestes r e c t a n g u 1 a r i s : .1, gills, moi-e 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. seyen-jointed. Labium []il.l4. fig.c] long and exceedingly 

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

 but dependent, and not closely applied to the yentral 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 leyel of the 

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

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

 angle just beyond its base, haying 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- 



