PLECOPTERA OF NORTH AMERICA 87 



Perla aestivalis, new species. 



(Plate 14, fig. 5; plate 18, fi^s. 7, S, 9, 10.) 



Length to wing tips, male, 10 mm. ; female, 12 mm. Ex- 

 panse, male, 18 mm. ; female, 20 mm. 



Color pale brown varied with pale yellow. Head brown- 

 ish with three spots in a row across the head that are 

 separated by the rear ocelli and the lateral ones of the 

 row are dilated around the eyes. Another larger spot be- 

 fore the middle ocellus is more or less extended at the 

 sides around the forward angles of the sinuous M-mark. 

 There are also some obscure yellowish touches along the 

 occipital border. Antennae and palpi brown. 



Prothorax subquadrangular with all angles somewhat 

 rounded, front margin broadly rounded, hind border 

 slightly concave in the middle. Sides of the disc rather 

 uniformly brown and with few slender obscure vermicu- 

 late embossed lines. Middorsal stripe of yellow rather nar- 

 'row, somewhat widened toward the rear end and hardly 

 continued upon the mesothorax. Legs brown. Wings yel- 

 lowish hyaline with pale brown veins. 



Abdomen pale brown, darker at sides, toward the tip 

 and before the genitalia. Tails brown. 



Male. Abdominal segments normal to the 7th whose 

 sternite is slightly prolonged in the middle into a low 

 broadly rounded lobe with a correspondingly broad notch 

 at either side of it. The 9th segment is moderately pro- 

 longed beneath into the. usual scoop-like upturned sub- 

 genital plate following. Segment 10 included in 9 below, 

 broadly divided above by a median apical cleft, the hind 

 angles of the cleft tergum being subtriangular with 

 broadly rounded tips. The U-shaped supra-anal process 

 possesses two long slender lateral stylets and its basal 

 attachment is a subtriangular chitinous plate in the base 

 of the wall of the 10th tergite, having the rear angles of 

 the triangle cleft at the tip. 



Female. The subgenital plate is long, its tip reaching 

 well across the 10th sternite, broadly subtriangular with 

 convex sides and rounded apex. The eggs of this species 

 are carried extruded in a rounded mass beneath the tip 

 of the abdomen. They are of a curious, lenticular form 

 (PI. 18, fig. 9). 



This species is very close to the eastern Pcrla duplicate! 

 Banks, but is paler, slenderer, and smaller. 



Holotype male, allotype female, Yellowstone National 

 Park (R. Muttkowsky, in Cornell University Collection). 



