179 



I have examined many specimens obtained by Mr. B,. Kennicott at 

 different points in British America, from Lake Winnipeg to the Great 

 Slave Lake, and by Mr. Drexler upon the southeastern shore of 

 Hudson Bay, all of which were kindly placed in my hands for exam- 

 ination by W. H. Edwards, Esq., of Newburgh, N. Y. I have also 

 had before me in my comparisons specimens in the Museum of Com- 

 parative Zoology at Cambridge, from various points in the northern 

 United States, among which are those collected by Professor Agassiz 

 on the north shore of Lake Superior ; besides these, I have availed 

 myself of my opportunities of studying the specimens contained in 

 the cabinet of the late Dr. Harris, now in possession of this Society, 

 and have, in addition, compared with them specimens in my own col- 

 lection, obtained in various portions of the New England States. 



I have never seen a perfectly white specimen of this insect ; the 

 most immaculate ones I have examined had a few gray scales scat- 

 tered about the base of the primaries and along the basal half of the 

 costal border, while beneath, the whole surface of the secondaries was 

 bathed with a scarcely perceptible tint of a pale-yellowish color ; 

 from this limit every possible intermediate variation may be found, 

 in males and females equally, till it comes to have an upper surface 

 with obsolete spots similarly situated to those on the upper surface of 

 P. Rajjce of Europe, and the line along the costal border extending 

 sometimes, with much distinctness, beyond the tip, nearly half way 

 down the outer border ; the upper surface is also sometimes faintly 

 tinged with pale-greenish yellow, the extremities of the nervules 

 tipped with black, and the grayish scales of the base extended into 

 the secondaries ; but upon the under surface are found the widest 

 limits of variation, for not only may the tips of the primaries become 

 distinctly greenish or lemon-yellow, and the nervules at the apical 

 portion, together with the median nervure, be somewhat heavily bor- 

 dered with grayish scales, but also the whole surface of the secondaries 

 may have its ground color distinctly greenish or lemon-yellow, and all 

 the nervures, from origin to tip, very broadly and thickly bordered 

 with grayish scales, while a slender line of grayish scales — the con- 

 tinuation of the third superior nervule — crosses the cell longitudi- 

 nally ; the costal border also at base is colored with orange, and the 

 inner border at base with grayish scales ; at the same time specimens 

 are found with the under surface of the secondaries having broadly 

 bordered nervures combined with a basal color of nearly pure white. 



No possible step in the gradation from one extreme to the other is 

 wanting, and both extremes are found equally among numerous ex- 

 amples from as widely distant places as Massachusetts and the Great 

 Slave Lake, though the suite of specimens with which I have made 

 my comparisons would seem to indicate that the paler forms are g^ore 

 commonly met with in the more southern localities, and the more 



