Order PLECOPTERA. 



The "Stone flies" which constitute this order are loose-jointed, flattened, 

 soft-bodied creatures with long net veined wings, the hind pair longitudinally 

 folded beneath the anterior. The head is large, the rnouth parts soft, antennae 

 long and tapering, eyes rather prominent. The prothorax is free and quadrate, 

 the other segments loosely joined. The abdomen is soft and usually with anal 

 filaments or processes. These "flies" are found along the streams and rivers 

 in which their larvae occur, resting on the leaves and not easily disturbed ; their 

 flight is heavy and they do no feeding upon living plants so far as known. The 

 larvae live in the streams under stones to which they cling so closely that, being 

 flattened, they are easily overlooked. They breathe by means of lateral gill 

 tufts which occur also on the head and which, in some species, persist even in 

 the adult stage ; a curious reminder of ancient conditions and an indication of 

 the low type of the order. The pupa is active and the transformation incom- 

 plete. 



It is very probable that many more species occur than we have yet found, but 

 what is already known shows that they form an important part of the aquatic 

 fauna in numbers as well as species, though of no importance to the agri- 

 culturist. 



Fig. 11. — A stone-fly and its larva ; Perla sp , enlarged. 



Family PERLIDiE. 



PTERONARCYS Newn. 

 P. nobilis Hagen. New York to Tennessee. 

 P. regalis Newn. Philadelphia. 



(39) 



