PLECOPTERA OF NORTH AMERICA 115 



Alloperla lamba, new species. 



(Plate 14, fig. 4; plate 22, figs. 8, 9.) 



Length to tip of wings, female, 9-10 mm.; expanse, 

 male, 16-18 mm. Length to tip of wings, female, 10.5-12 

 mm.; expanse, female, 18.5-21 mm. 



General color very similar to color adensis, yellow, with 

 dark spots on head, with the margin and rugosities of 

 pronotum dark and with abdomen dark brown. 



Head hardly wider than prothorax ; yellow with a dark 

 V-shaped mark connecting the ocelli, with the frontal M- 

 ridge, the lateral tubercles and clypeus dark brown ; also 

 a dark spot behind the eye. (There is quite a little varia- 

 tion in the size of these dark markings.) Hind ocelli a 

 little closer to the eyes than to each other ; antennae yel- 

 low at the base, blackish toward the tip. 



Prothorax transversely oval, almost twice as wide as 

 long ; yellow with a narrow blackish margin and with the 

 rugosities dark brown. Legs yellowish to brownish, tarsi 

 darker at the tip. Wings greenish to slightly brownish 

 infuscated, veins mostly brown. Meso- and metanotum 

 dark brown. 



Abdomen brown, with a darker median dorsal stripe 

 and with the posterior margins of the tergites darker. 

 Cerci yellowish or light brown. 



Male. Tenth abdominal tergite widely and deeply cleft ; 

 ninth tergite quite deeply emarginate behind and on the 

 anterior margin with a transverse raised, triangularly 

 notched tubercle; supra-anal process recurved, nearly 

 three times as long as its greatest width (dorsal view), 

 with a dorsal, median, membranous carina; at the tip 

 with a slender, slightly upturned, process which orig- 

 inates from the lower anterior portion of the supra-anal 

 process ; penis at the tip bilobed and near the base with 

 a dorsal bilobed, flattened, black, longitudinally stri- 

 ated appendage which is wider than long (when the penis 

 is retracted this chitinized lobe can usually be seen from 

 below through the ninth abdominal sternite) ; subanal 

 lobes small, unmodified; ninth sternite produced and 

 truncate behind. 



Female. Subgenital plate of eighth sternite somewhat 

 triangularly produced and behind broadly rounded; 

 clothed with long hairs. 



Holotype male, allotype female, Aug. 3, 1921, Fern 

 Lake, Estes Park, Colo. (P. W. Claassen, Cornell Uni- 

 versity Collection). Paratvpes, 33 males, 34 females, 

 Aug. 3, 1921, Fern Lake, Estes Park, Colo. (P. W. C.) ; 



