PLECOPTERA OF NORTH AMERICA 35 



Females. 



1. Posterior margin of the subgenital plate but 



little produced backward 2 



Posterior margin of the subgenital plate conspic- 

 uously extended backward, with teeth or proc- 

 esses 3 



2. Margin entire dorsata 



Margin with a small rectangular median ex- 

 cision nobilis 



3. Bearing a pair of flat triangular processes on its 



ventral side 4 



Bearing very slender or very minute processes. _ 5 



4. Entire sternite deeply cleft to form the two 



broad processes biloba 



Processes upon the apex of the subgenital plate 

 that arises before the apical margin of the 

 sternite 6 



5. The processes are somewhat equilateral triangles 



approximated at base calif omica 



The processes are very elongate triangles, twice 

 as high as broad and more widely separated at 

 base princeps 



6. Processes arise before the apex of the segment 



and are slender and recurving, and as long as 



the segment proteus 



Processes a minute pair of teeth at the apex of a 

 broadly ovate lobe that extends beneath seg- 

 ment 9 ' comstocki 



Pteronarcys dorsata Say. 



(Plate 7, figs. 1, 2, text fig. 10.) 



1823. Sialis dorsata Say, West. Quart. Rept., 2:164. 



1838. Pteronarcys regalis Newman, Ent. Mag., 5:176. 



1917. Pteronarcys dorsata Smith, Trans. Am. Ent. Soc, 43:446. 



(contains full bibliography of adult and nymph, 30 titles). 



Male. Length to wing tips 40-47 mm. ; of antennae 22- 

 25 mm. ; of tails 10-13 mm. ; expanse of wings 70-80 mm. 



Female. Length to wing tips 50-60 mm. ; of antennae 

 22-26 mm. ; of tails 12-15 mm. ; expanse 86-106 mm. 



The largest known stonefly. Dark brown, paler beneath 

 and with indistinct yellowish intersegmental markings. 

 Prothorax as wide as the head and slightly widened pos- 

 teriorly, front margin and sides straight, its hind margin 

 convex, and its angles abruptly produced in small tooth- 

 like projections. The middorsal yellow line upon the disk 

 is widened toward its ends and somewhat interrupted in 



