AQUATIC INSECTS IN NEW YORK STATE 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, cylindric ab- 
Fig.7 Nymphof Lestes rectangularis; 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 [pl.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 pl.14, fig.d], bent almost at a right 
‘angle just beyond its base, having a very large movable hook, be- 
iyond 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- 
