AQUATIC INSECTS IN NEW ^ORK 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, 

 lialf as wide as long, with short, stout, movable hook and 

 small end hook separated h\ 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 ofArgia 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. 



