94 THE BUTTERFLIES OF THE WEST COAST 



b, Female, Summit, Cal., 1,500 feet altitude, June, 

 1892; Author, 

 bb, Female, underside, Tallac Peak, 10,000 feet alti- 

 tude, July, 1892; Author. 

 Flava is supposed to be a dimorphic female of Sisymbri, no 

 male having yet been found, and always yellowish in color, like 

 these figures. But it would not surprise me to know that there 

 is a male, and that it is a sort of a twin species to Sisymbri. It 

 seems to inhabit higher altitudes than Sisymbri by 2,500 to 3,000 

 feet, and to be absent at Sisymbri's lower ranges. 



No one has ever bred the larvae of Flava, nor is the larval food- 

 plant known, though presumably it is any one of the cruciferous 

 plants ; the egg, also, has never been described ; it must, however, 

 be fertile, judging from analogy, for other dimorphic females are 

 always very prolific, tending to out-breed the normal-colored 

 females. 



37. Pieris Nelsoni. Not elsewhere illustrated in accessible form. 



P>LATE V ; Figure 37. 



Of Nelsoni only one male specimen has ever been taken ; that 

 one by Mr. Nelson, at St. Michaels, Alaska. The figure here 

 shown is a photographic copy of a pen-drawing by Miss Colgan, 

 of the lithograph figure of Mr. Edwards, published in 1883, in his 

 Butterflies of North America, an expensive work, and inaccessible 

 to most people. 



The right-hand wings are the upperside, and the left-hand ones 

 are the underside. The pen.-drawing is well done, as an error 

 which crept into the drawing made by the lithographer, as the 

 expert lepidopterist will perhaps notice, is faithfully copied. 



38. Pieris Occidentalis. 



Plate V ; Figures 38, b. 



Fig. 38, Male, Ellensburg, Eastern Washington, May, 1890; 

 Author. 

 b, Female, Sierra Nevadas, Cal., 7,000 feet altitude, 

 1892 ; Author. 

 Occidentalis is a very common butterfly all over the whole west- 

 ern part of the United States, west of the Rocky Mountains ; being 

 rather a cold species, and loving the more northern parts bet- 

 ter than the southern. On the immediate Coast it is not seen much 



