438 
NORTH AMERICAN PLECOPTERA 
make them of little value in identification, but the structural 
modifications in genitalia serve as excellent specific characters. 
A few are generic; in the male, the tenth tergite is bifid (fig. 1), 
the supra-anal plate is remarkably modified, it is either produced 
and curved ventralward as a sperm-conveyer (fig. 1 Sup. A. P.), 
or it is an erect, probe-like organ (fig. 12). In the female the tenth 
tergite is entire, narrow below, and above produced into a tri- 
angular process; the supra-anal plate is a fleshy lobe attached to 
the ventral surface of the tenth dorsal segment (fig. 2 Sup. A. P.) 
and the sub-anal plates are triangular (fig. 2 Sub. A. P.). 
We have representatives of all the North American species. 
Some species are represented by pinned specimens only, others 
by alcoholics as well. Wherever possible the latter are used for 
structural characters, and the dry specimens for color markings. 
Nymph 
Large (1| in.), stout-bodied, concolorous nymphs with smooth 
bodies; long, slender antennae; short, stout, tapering setae; easily 
distinguished from all other stone-fly nymphs (except those of 
Pteronarcella, a genus of much smaller individuals) by the pres- 
ence of tracheal gills on the basal segments of the abdomen. 
Dark brown, head narrower than the prothorax, and slightly 
covered by its front margin. Three small ocelli forming an 
equilateral triangle; the distance from the lateral ocelli to the 
inner margin of the eyes equal to the distance between the ocelli. 
On either side of the ocellar triangle a round, rufous spot, a smaller 
and less conspicuous one anterior to it, a rufous V-shaped mark 
opening forward with its base in the median ocellus. The occip- 
ital margin with reticulate corrugations. Antennae long and 
tapering, well developed supra-antennal plates. 
Prothorax about twice as wide as long; its sides flaring, the 
four angles produced. The three thoracic segments obscurely 
marked with rufous on the disc. Legs, stout; the distal end of 
the femur triangularly notched on the inner surface; the segments 
of the tarsus of unequal length, the second segment the shortest, 
half as long as the first; the third, as long again as one and two 
taken together. 
Abdomen cylindric, the tenth segment narrow below, pro- 
longed above into a median, conical process; the supra-anal 
