458 
NORTH AMERICAN PLECOPTERA 
Among these are the considerably shortened inner end (fig. 
E, I) and the greater development of the lateral braces (fig. E, 
L. B.). In size the braces are not relatively larger than those in 
Pt. 'proteus, blit the}^ are much more heavily chitinized and con- 
sequently much stronger. It seems probable that the reduction 
of the inner end has necessitated some such lateral extension to 
strengthen the place of attachment of the supra-anal within the 
body. The relative position, attachment and muscular con- 
nection (fig. E, M) of the para-genital plates (fig. E, P. G. P.) is 
the same as in Pt. proteus. The free end (fig. E, F) is curiously 
modified at the extremity. It is made up of a pair of partially 
chitinized semi-elliptical plates, attached to each other at the 
posterior margins only, just ventral to the base of these hangs a 
pair of delicate heart-shaped memliranous sacs. Just what the 
function of such a structure might be is puzzling. It is probably 
of accessory nature and here again the presence of a true penis 
on segment nine, connected with the sperm-ducts is assumed. 
Keys to Species of Pteronarcella 
Adults 
Males 
a. The dorso-lateral posterior margin of the second segment without a 
conspicuous rounded knob (knobs conspicuous only on segments four or five 
to nine), the ninth dorsal segment with a broad scoop, sub-anal plates dark 
brown regularis 
aa. The dorso-lateral posterior margin of the second segment with a con- 
spicuous rounded knob (segments two to nine with prominent knobs), the 
ninth dorsal segment with a shallow, narrow scoop, subanal plate whitish. 
torosa 
Females 
a. The entire length of the eighth ventral segment involved in the formation 
of the vulvar lamina, and the median area of the posterior border produced. 
(The vulvar lamina with a trilobed tip or a single lobe.) 
b. A single lobe with a more or less conspicuous notch in the tip. regularis 
bb. A trilobed tip, the middle lobe the longest triloba 
aa. The posterior border only of the eighth ventral segment involved in the 
formation of the vulvar lamina, the median area not produced. (A rounded 
knob on either side of the median area, the part between the notches, a narrow 
lobe not reaching the border of the segment) badia 
