56 THOMAS SAY FOUNDATION 



up to the edge of the middle stripe, more openly spaced 

 toward the yellow line at the side margin. Similar small- 

 er marmorations besprinkle the large yellow areas upon 

 the sides of the occiput. There is a short narrow pale 

 stripe on the praescutum of the mesothorax, and a still 

 paler spot before each wing root. Legs pale with a wash 

 of brown near the ends of femora and tibiae and tip of 

 tarsi ; knee yellowish, between the bands of brown. Wings 

 smoky hyaline with brown veins, abdomen brownish, 

 darker on the sides. 



Male. Segments normal to the 9th abdominal, which 

 is twice as long on the ventral as on the dorsal side, its 

 sternite prolonged rearward in a broad genital scoop with 

 a short longitudinal fold or sulcus demarking its sides. 

 Middorsal margin slightly elevated, reflexed, and thick- 

 ened and beset with short stiff yellowish hairs. The 10th 

 segment is divided on the middorsal line to accommodate 

 the remarkably enlarged supra-anal process; the top of 

 each half is again divided transversely by a deep oval 

 cleft, the edges of which are fringed with stiff yellowish 

 hair ; the shorter anterior division before the cleft is nor- 

 mally concealed within the apex of the 9th segment ; the 

 longer posterior division is curved forward and, with its 

 fellow of the opposite side, constitutes the genital hooks. 



Female. The subgenital plate is prolonged to cover the 

 ventral surface of the 9th segment, divided into two 

 broad, evenly rounded lobes, between which is a narrow, 

 parallel-sided square-cut notch ; its bottom is at the level 

 of the apex of the 8th segment. 



This is the common species of our western mountains. 

 In the original description Hagen (1. c. p. 576) called at- 

 tention to the five pairs of gills that the adult insect car- 

 ries over from the last nymphal stage. 



Distribution. — Colorado, foothills; Tolland, Colo. (G. S. 

 Dodds) ; Kenosha Pass, August and Platte Canon, Colo., 

 July (Osier) ; Lawn Lake, Estes Park, Colo. (P. W. Claas- 

 sen) ; Custer Co., Colo. "A 25" brachvpterous male (T. 

 D. A. Cockerell) ; Salt Lake Co., Utah, June 10, 1910; 

 Rogers Pass, B. C., 4500 ft. to 5525 ft. elevation, males 

 and females, August 19, 1908 (J. C. Bradley) ; Howser, 

 Selkirk Mts., B. C, June 22 (J. C. Bradley). 



Perlodes yosemite new species. 



(Plate 7, fig. 20; plate 10, fig. S.) 



Male. Length of body 13 mm.; of antennae 11 mm.; 

 of tail 10 mm. 



