106 THOMAS SAY FOUNDATION 



Key to the Species of Alloperla. 



Males. 



1. Tenth tergite with an inward pointing hook each 



side at the base of tails; supra-anal process in- 

 distinct, very short, largely membranous, with 



a small rounded knob at tip 2 



Tenth tergite without inward pointing hooks at 

 base of cerci; supra-anal process distinct, us- 

 ually long and heavily chitinized 3 



2. Western species pallidula 



Eastern species marginata 



3. Eighth abdominal tergite (antepenultimate seg- 



ment) with a raised, notched tubercle ; supra- 

 anal process broadly spatulate; sides of pro- 



notum black pacifica 



No tubercle on eighth abdominal tergite (though 

 a tubercle is often present on the anterior mar- 

 gin of the ninth tergite) 4 



4. A distinct, raised chitinous tubercle on the ninth 



abdominal tergite (penultimate segment) 5 



Ninth abdominal tergite without a distinct raised 

 tubercle 12 



5. Yellowish, with lateral margin of pronotum 



blackish, rest of pronotum and head yellowish ; 

 supra-anal process either very long and slender 

 or else flattened and evenly rounded at the tip ; 



mostly Eastern species 6 



Yellowish with the rugosities on prothorax 

 blackish and with blackish markings on the 

 head (continua Bks. usually with a dark median 

 stripe on head and prothorax) supra-anal proc- 

 ess not long and slender (except boreal is, the 

 largest species of the genus) 7 



6. Supra-anal process very long, slender, upturned 



lateralis 



Supra-anal process short, flattened, broad, and at 

 the tip evenly rounded novascotiana 



7. Tubercle on ninth tergite deeply notched; supra- 



anal process much enlarged beyond the base 

 and at the apex with a sharply pointed small 



process 8 



Tubercle on ninth tergite not distinctly or deeply 

 notched ; supra-anal process rather slender and 

 without a sharply pointed tooth or process at 

 the tip 10 



