34; THOMAS SAY FOUNDATION 



(Stett. Ent. Zeit. for 1877, pp. 477-489) records some ob- 

 servations on the mating habits of the latter species. The 

 senior author in 1923 observed P. princeps emerging from 

 the streams in Andreas Canon, San Jacinto Mts., Cali- 

 fornia. The imagos left their cast-off skins clinging to the 

 down-stream face of the huge granite boulders that stood 

 partly immersed in the water, and themselves imme- 

 diately sought shelter in less exposed places, usually about 

 the log-drifts in the stream. 

 Genotype, Perla dorsata Say. 



Key to the species of Pteronarcys. 



Males. 



1. Ninth abdominal sternite prolonged backward 



far beyond the tip of the tenth segment and 

 bifid at the tip of the prolongation. Tenth ab- 

 dominal tergite divided and produced backward 



in two appendage-like lobes 2 



Ninth abdominal sternite truncate, but little pro- 

 duced and entire on tip. Tenth tergite divided 

 into two erect more or less rounded lobes 3 



2. Tips bordering the notch in the apex of the 



ninth sternite straightish, not decurved. Tips 

 of the appendage-like divisions of the tenth ter- 

 gite upcurved dorsata 



Tips bordering the notch in the apex of the ninth 

 sternite decurved. Tips of the appendage-like 

 divisions of the tenth tergite straightish, 

 scarcely curved upward nobilis 



3. Supra-anal plate huge, decurved, laterally flat- 



tened and forked under the tip 4 



Supra-anal plate slender, almost spinous, erect 

 or curving forward 5 



4. Erect lobes of the divided tenth tergite rather 



broadly rounded californica 



Erect lobes of the divided tenth tergite rather 

 narrow, much higher than wide princeps 



5. An anteriorly-directed median dorsal process 



arising from the rear and lying upon the ninth 



tergite proteus 



No such process present; 9 rounded above--biloba 



