:*2 THOMAS SAY FOUNDATION 



Family PTERONARCIDAE. 



This is a small family of mostly large stoneflies in- 

 cluding in our fauna but two genera. They are distin- 

 guished from other stoneflies of our fauna by reticulate 

 venation extending in the fore wing from the front all 

 the way rearward across the anal veins. There is no dis- 

 tinct transverse cord developed. The wings are dusky 

 with veins of darker brown. Brachypterous males occur 

 in at least one species of Pteronarcella. Legs rather long, 

 with middle segment of the tarsus half as long as the 

 basal segment. The mandibles in the adult are rudi- 

 mentary and the segments of the palpi appear to be mul- 

 tiarticulate, their walls being made up of many irregular 

 chitinous half rings. The mandibles of the nymphs are 

 heavy and stoutly toothed at the apex, adapting them for 

 feeding upon the vegetable trash that gathers in the 

 eddies and at the sides of streams. The gills are in pedi- 

 cellate tufts, on the ventral side of the thoracic end of 

 two or three terminal segments ; and so slight is the 

 transformation that these are carried over into adult 

 life as small but readily recognizable rudiments. The 

 supra-anal process of the male is highly developed as an 

 accessory organ of reproduction, and the tenth abdominal 

 segment is in this sex greatly reduced and almost in- 

 cluded within the expanded and ventrally produced rear 

 end of the ninth segment. The genus Pteronarcys is dis- 

 tributed across the continent and into northern Asia. The 

 genus Pteronarcella is known only from the mountains of 

 the western United States. 



This family, having recently received adequate treat- 

 ment at the hands of Lucy Wright Smith (Trans. Am. 

 Ent. Soc. 43: 433-463, 1917), we have given it rather 

 brief treatment, especially as to bibliographic and distri- 

 butional records, and our figures for the species of Ptero- 

 narcys are copied from her plates. 



Key to the North American Genera of Pteronarcidae. 

 1. Large species (IVi to 2V-> inches in length) ; forewing 

 with two rows of cross-veins in anal field, with cross- 

 veins between R and Rs and between Rs and M be- 

 fore the cord ; hind wing with more than 10 long 



branches of anal veins Pteronarcys 



Smaller species (one inch or less) forewing with only 

 two rows of crossveins in anal field ; no crossveins 

 between R and Rs and M before the cord ; hind wing 

 with fewer than 10 long branches of anal veins. 

 Pteronarcella 



