AQUATIC INSECTS IN NEW YORK STATE 239 
middle legs; the mentum is less than a third longer than 
wide; median lobe spinulose on its prominent free border; 
no mental setae; lateral setae one to four; lateral lobe short, 
half as wide as long, with short, stout, movable hook and 
small end hook separated by a more or less distinct notch from 
the inner margin, and with one or more smaller teeth on the 
distal end above the end hook. 
.Prothorax pointed anteriorly and fitting the rear emargina- 
tion of the head. Mesothorax and metathorax much thicker, 
Fig. 9 Outline of head of nymph of Argia apicalis 
with the wings borne at a considerable elevation. Legs short, 
usually banded transversely, and bearing spines as well as 
hairs. 
Abdomen stout, somewhat tapering, and with its segments 
decreasing in length to the ninth, the tenth again a little longer. 
Gills oblong about half as long as wide, obtuse at apex 
and generally with paler apical markings. Among alcoholic 
specimens frequently, and among fresh specimens occasion- 
ally, the gills are absent, being easily broken off. If their 
loss occur early in nymphal life, they are regenerated, and it 
is no uncommon thing to find a specimen with one, two or 
three of the gill plates of smaller size than the normal. The 
loss of the gills seems not to affect seriously the respiration 
of the nymphs. 3 
