444 
NORTH AMERICAN PLECOPTERA 
opening ventral to them instead of between them. Thus Hagen’s 
term, “para-anals,” for the distal portions is not applicable here. 
Consequently I have termed the entire plates para-genitals. 
A change of function has presumably accompanied the change 
in form of the free end of the supra-anal. It seems rather likely 
that it may be used as a probe-like organ in opening up the genital 
passage of the female. Since the supra-anal plate is apparently 
entirely accessory, the placing of the spermatazoa into the body 
of the female must take place in another way, probably by means 
of a true penis — one directly connected with the sperm ducts. 
Such a penis has been observed in Perla immarginata} Here it 
is a soft, fleshy, contractile organ entirely concealed within the 
body except at the time of copulation, when it is protruded from 
the posterior border of the ninth sternite. The same kind has 
been found in Isogenus frontalis and Perla decipiens, and is un- 
doubtedly the more common, and more primitive structure for 
the transference of spermatozoa in stone-flies. 
Keys to Species of Pteronarcys Newman 
Adults 
Males 
a. The ninth ventral segment elongate, with a notched tip, the tenth tergite 
bifid and its two lobes elongate, appendage-like. 
b. Tips of the notch at apex of the ninth sternite straight or curved ventral- 
ward. 
c. Tips of the notch at apex of the ninth sternite straight. Tips of the 
tenth tergite strongly bent upward, emarginate on opposed inner 
edges dorsata 
cc. Tips of the notch at apex of the ninth sternite curved ventralward. 
Tips of the tenth tergite only slightly curved dorsalward, inner mar- 
gins entire nobills 
aa. The ninth ventral segment truncate, the tenth tergite bifid with rounded 
lobes. 
b. Sub-anal plates broadly triangular, supra-anal plate developed as a 
sperm-conveyer of remarkable form, curved ventralward. 
c. Lobes of the tenth tergite, large, erect; sperm-conveyer flat above. 
californlca 
cc. Lobes of the tenth tergite, small, erect; sperm-conveyer, evenly 
rounded above princeps 
bb. Sub-anal plates spoon -shaped, supra-anal plate modified in the form of 
an erect probe. 
^ The Biology of Perla immarginata Say. L. W. Smith, Annals Ent. Soc. 
Amer., 6: 1913. 
