456 
NORTH AMERICAN PLECOPTERA 
Prothorax about square, perhaps a little wider than long, 
angles rounded, not produced, the disc corrugated; the three 
thoracic segments very dark above, paler beneath. Wings very 
much reduced in size in the males of some species, veins brown. 
The inner surface of the femur with a triangular groove, its base 
at the distal end, the segments of the tarsi of unequal length, 
the second the shortest, half as long as the first, the third as long 
as one and two taken together. 
Abdomen cylindric, paler beneath. Setae long and slender, 
bases stout, the first five basal segments very short. Seventeen 
pairs of tracheal gills, small and inconspicuous, carried over from 
the nymph. 
Male. The ninth segment very much elongated above and 
below, entirely concealing the tenth segment and the supra-anal 
plate (fig. 28); sub-anal plates conspicuous (fig. 28, Sub. A. P.). 
Female. The tenth segment narrow below, triangularly pro- 
duced above, the supra-anal plate a rounded fleshy lobe attached 
to the ventral surface of the tenth tergite; sub-anal plates tri- 
angular (fig. 29). 
• Nymph 
Nymphs very similar to Pteronarcys but readily distinguished 
from them by their smaller size (when grown about three-fourths 
inch), and the presence of a pair of tracheal gills on the third 
segment of the abdomen, as well as a pair on each of the first 
two segments, as in Pteronarcys. 
Color nearly uniform, brown. Head rather triangulai, much 
narrower than the prothorax; three small ocelli forming an equi- 
lateral triangle; paler, inconspicuous markings on this disc, 
antennae slender, tapering, a little less than half the length of 
the body; supra-antennal plate narrow. 
Prothorax considerably broader than long; sides, flaring, con- 
vex, angles well rounded, more or less obsolete embossed markings 
on the disc. Legs stout, the inner surface of the femur with a 
triangular groove, its base at the distal end; the segments of the 
tarsi of unequal length, the second is the shortest, and is half as 
long as the first, the third is twice as long as the first two taken 
together. 
