PLECOPTERA OF NORTH AMERICA 73 



humps on the dorsum not so fully developed: they are 

 usually distinct only on segments 8 and 9 (these are, how- 

 ever, very variable in appearance) ; and there seems to be 

 the difference in the conformation of the tip of the supra- 

 anal process that is shown in our figure in Plate 11 (fig. 

 5). 



The subanal plate of the female is similar to that of /. 

 frontalis, but its tip is usually more squarely truncated, 

 and its dividing median notch is narrower. 



A further study of the range of variability of the three 

 preceding may determine that they constitute but one 

 variable species. 



The eggs of all of them are roundish oblong with a low 

 wide reflexed collar at the micropylar end, this collar hav- 

 ing about a fourth the width of the egg. In typical speci- 

 mens of /. frontalis from Grand Lake, Newfoundland, the 

 body of the egg is a trifle wider than in specimens ol /. 

 colubrinus from the Columbia River. 



Distribution. — Snake River, Idaho; The Dalles, Ore., 

 June 23 (Hubbard and Schwarz) ; Umatilla, Ore., June 

 24 (S. Henshaw) ; Pullman, Wash., May 18, 1908 ; Rifle, 

 Colo., June 23, 1904; Apostle Islands, Ashland Co., Wis., 

 July 4-11; Port Huron, Mich., June (Hubbard and 

 Schwarz) ; Medicine Hat, Assnba., June 13, 1905 ; Car- 

 bonate, B. C, Canada at 2600 ft. elevation (J. C. Bradley) 

 Glenora, B. C. ; Upper Mackenzie River (Kennicott) ; 

 Ungva Bay, H. B. T. (L..M. Turner). 



Genus PERLA Geoffroy. 



1764. Perla Geoffroy, Hist. Ins.. 2:229. 



1842. Perla Pretet, Perlides, p. 141. 



1923. Perla Klapalek, Coll. Zool. Zelys, IV, 2, p. 35. 



A somewhat heterogeneous group of mostly rather 

 large stoneflies having little else in common than the dor- 

 sally cleft 10th segment of the male abdomen : often, a 

 supra-anal process of variable form occupies the cleft. 

 There is a series of species (hastata and bilobata) having a 

 rectangular prothorax with a median yellow stripe, radial 

 sector forking far out, erect, well matched cord, and cu- 

 bito-anal crossvein well beyond the apex of the anal cell. 

 There is another contrasting series of species having the 

 prothorax narrowed to rear and with rounded hind 

 angles, lacking the median yellow stripe, radial sector 

 more deeply forking and cord swung outward and the 

 cubito-anal crossvein situated at or before the apex of the 

 anal cell. Numerous divisions of the genus have been pro- 



