316 LEPIDOPTER A OF NORTH AMERICA. 



shore of Hudson's Bay, all of which were kindly placed in my hands 

 for examination by W. H. Edwards, Esq., of JSTewburgh, N. Y. 

 I have also had before me in my compai'isons specinaens in the 

 Museum of Comparative Zoology at Cambridge, from various 

 points in the northern United States, among which are those col- 

 lected by Professor Agassiz, on the north shore of Lake Superior ; 

 besides these, I have availed myself of my opportunities of study- 

 ing 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 collection, 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 second- 

 aries was bathed with a scarcely perceptible tint of a pale-yellow- 

 ish 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. Rapce of Europe, and the line along the 

 costal border extending sometimes, with much distinctness, beyond 

 the tip, nearly halfway down the outer border; the upper surface 

 is also sometimes faintly tinged with pale-greenish yellow, the ex- 

 tremities of their nervules tipped with black, and the grayish scales 

 of the base extended into the secondaries ; but upon the under 

 surface are found the widest limit 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 

 medial nervure, be somewhat heavily bordered 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 continuation of 

 the third superior nervule — crosses the cell longitudinally ; 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 bor- 

 dered 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 



