Family PTERONARCIDAE 
The nymphs of this family are readily distinguished from all 
other stoneflies. They are the only ones that have tufts of gills 
on the first two or three ventral abdominal segments. Their bodies 
are cylindrical and their color is almost uniformly brown to 
blackish. 
Head rather small, narrower than prothorax; three ocelli 
placed in an equilateral triangle; antennae long and slender with 
prominent antennal plates; occiput rugulose; anterior to the ocel- 
lar triangle a reddish V-shaped or M-mark. Mouth parts well 
developed for masticating the vegetable food on which they 
subsist. 
Labrum narrow, about twice as wide as long. 
Mandibles asymmetrical; the left mandible with five unequal 
teeth followed mesad by a well-developed molar beyond which 
there is a tuft of hairs; the right mandible usually possesses 
only four unequal teeth. 
Maxillae: maxillary palpus stout, five-segmented; galea rather 
broad, and made up of two segments—a short basal, and a large 
apical segment—tipped with a bunch of spinules; lacinia triden- 
tate ; cardo about half as long as the stipes. 
Labium much longer than wide, with glossae and paraglossae 
subequal; the three-segmented palpus stout; mentum a small, 
narrow transverse triangular band; submentum very large with 
a sinuated posterior margin; hypopharynx rounded, hairy, and 
projecting beyond the tip of the glossae. 
Pronotum about twice as wide as long, the sides somewhat 
flaring and the angles usually more or less produced; surface 
somewhat rugulose. Legs stout; segments of tarsus unequal, the 
second about half as long as the first, and the third more than 
twice as long as one and two combined; margins of femur and 
tibia with a fringe of hairs. Wing pads well developed. 
Abdomen eylindriec, the abdominal segments either smooth or 
with lateral teeth or hooks. Cerei hardly ever more than half as 
long as the body. Thirteen to seventeen pairs of tufted gills, 
located on the ventral side of the thorax and on the first two or 
three abdominal segments. 
General Distribution 
Quite universally distributed over North America (except 
Pteronarcella which is a Western genus) wherever small, cold, 
upland spring brooks may be found. 
