122 THOMAS SAY FOUNDATION 



produced into a large rounded subgenital plate which 

 normally reaches across the entire ninth sternite. In 

 some of the females the hind margin of the plate is 

 slightly emarginate while in others it is evenly rounded. 



Distribution. — Type No. 11351, female, Pullman, Wash. 

 (Banks Coll., Mus. Comp. Zool., Cambridge, Mass.) ; one 

 male, Pullman, Wash. ; one male, one female, June 22, one 

 male, six females, July 14-15, Florissant, Colo. ; two males, 

 June 8, Troublesome, Colo. (S. A. Rohwer). All these in 

 Banks' Collection. Many males and females, Boulder, 

 Colo. (G. S. Dodd) ; one female, June 1, Platte Canon, 

 Colo. (Dyar and Caudell). 



Alloperla mediana Banks. 



(Plate 21, figs. 4, 5.) 

 1911. Alloperla mediana Banks, Trans. Am. Ent. Soc, 37:336. 



Length to tip of wings, male, 9-11 ; expanse, male, 16-19 

 mm. ; length to tip of wings, female, 10-12.5 mm. ; ex- 

 panse, female, 18-22 mm. 



General color pale yellow, with a more or less distinct, 

 brown median stripe on pronotum and a dark stripe on 

 abdomen. 



Head a little wider than prothorax, pale yellow with a 

 little blackish around the ocelli; hind ocelli a little closer 

 to eyes than to each other ; antennae yellow at base, dark 

 brown or blackish toward the tip. 



Prothorax transversely oval, half again as wide as 

 long; yellow, usually with a broad median dark stripe 

 which tends to fade out toward the margins ; surface of 

 pronotum not very rugose; legs yellow, tarsi a little 

 darker at the tip; wings yellowish or greenish hyaline, 

 veins yellowish. 



Abdomen yellow, with a wide, dark, median, dorsal 

 band. Cerci yellow, a little darker toward the tip. 



Male. Tenth abdominal te.rgite broadly and deeply 

 cleft; ninth tergite usually without a distinct median 

 raised tubercle although in some of the males there ap- 

 pears to be a small tubercle present. Supra-anal process 

 recurved, flattened laterally, at the base very broad (side 

 view) with a slender, upturned process at the tip ; subanal 

 lobes small, unmodified ; ninth sternite produced and al- 

 most evenly rounded behind. 



Female. Subgenital plate of eighth sternite somewhat 

 triangularly produced and behind broadly truncate ; the 

 plate often shows a median raised area. 



This species is quite closely allied to lateralis. 



