CLASSIFICATION 
SUMMARY OF CHARACTERS 
4 pew nymphs of Plecoptera are aquatic, living mostly in run- 
ning water. They are said to resemble the adults, but in some 
genera, such as Peltoperla for example, the resemblance of nymph 
to adult is quite remote. The mature nymphs range in size from 
the small Capniidae and Nemouridae, in which some species do 
not measure over six or seven millimeters in length, to the large 
nymphs of Pteronareys which attain a length of two inches or 
more. 
The general color of the nymphs is yellowish brown, to dark 
brown or blackish; or patterned with yellow and brown, or yellow 
and. black. 
Four of the five North American families (Pteronarcidae, Pelto- 
perlidae, Nemouridae, and Capniidae) may be said to be quite 
uniformly brown in color and in only one family (Perlidae) are 
found the brightly colored or more strikingly patterned nymphs. 
The general form of the body is elongate, subeylindrical, or 
considerably depressed, the nymphs of the Perlidae being, in gen- 
eral, more flattened than the nymphs of the other families. The 
body regions are well defined ; the pro-, meso-, and metathorax each 
are large and distinct, and the entire thorax is about as long as the 
abdomen. 
The head is more or less triangular in shape and is about as wide 
as, or a little wider than, the pronotum, except in the Peltoperlidae 
and the Pteronarcidae where the head is much narrower than the 
pronotum. The compound eyes are well developed and there are 
usually either two or three ocelli present. The V-shaped epicranial 
suture is not apparent in the Perlidae, but is distinct in all other 
families. The antennae are filiform, composed of many segments, 
and normally half, or nearly half, as long as the body. 
The mouth parts are of the chewing type and are strongly de- 
veloped. In general structure they resemble the Orthopteroid 
mouth parts. The labrum is wider than long and fringed with 
hairs on the anterior margin. In the Perlidae, the labrum bears on 
the median anterior area a fleshy epipharynx which is closely be- 
set with very fine bristles and may be rolled out or retracted. 
The mandibles are asymmetrical, more or less triangular in 
