166 THOMAS SAY FOUNDATION 



sharp or narrowly rounded ; hind angles mostly broadly 

 rounded ; surface with large, irregular, flattened rugosi- 

 ties. Legs yellowish to brownish ; first two tarsal seg- 

 ments very short, subequal, third segment very long, 

 much longer than one and two combined. Wings subhy- 

 aline to blackish inf uscated ; numerous costal crossveins ; 

 subcosta terminates before the cord ; the branches of Cul 

 in the f orewing usually originate from the anterior side ; 

 hind wing with a large anal field ; usually no cubital cross- 

 veins in hind wing, except the end ones. 



Abdomen with two short cerci. 



Male. Ninth abdominal sternite prolonged and evenly 

 rounded behind, bearing at or near the front mar- 

 gin a thickened button-like knob; from the base of the 

 knob two divergent lines to the posterior margin of the 

 ninth sternite, and the area between these lines usually 

 sunken; subanal lobes broadly triangular, upcurved; 

 supra-anal process developed into an upturned lobe, va- 

 riously modified. 



Female. Hind margin of eighth abdominal sternite 

 either unmodified or produced into a rounded or notched 

 subgenital plate. 



Genotype, Peltoperla arcuata Ndm. 



Key to the Species of Peltoperla. 



1. Western species; males with a transverse knob 



on the ninth abdominal sternite located some 

 distance back of the anterior margin; females 

 with a large, wide subgenital plate which covers 

 most of the ninth sternite and medially is 



notched 2 



Eastern species; males with a rounded knob on 

 the anterior margin of the ninth abdominal 

 sternite, the knob as wide as long; female plate 

 usually without a median notch, or when 

 notched the plate is only slightly produced 4 



2. Ocelli closer to each other than to the eyes ; wings 



usually heavily inf uscated ; a large species, 

 males, 18-21 mm. in length, females 23-26 mm. ; 

 male supra-anal process composed of a globose 

 membranous lobe; female plate broadly emar- 



ginate cora 



Ocelli closer to eyes than to each other; wings 

 not heavily inf uscated; size 9-18 mm. in length 3 



