59 



dark markings on the veins of underside; it is probable that these 

 two forms represent the spring and summer generations, but our 

 dated material from the type localities is too scanty to settle this 

 point. Wright's figures (1. c. PI. VI, Figs. 45b and 45c) possibly 

 represent marginalis as they were captured in May ; they are certainly 

 not venosa as he lists them ; his figures 45 and 46b represent the two 

 sexes of pallida. 



In Utah we meet with a second generation (July, August) which 

 is extremely pale, being practically immaculate in both sexes on both 

 sides; the underside is tinged with pale yellow on secondaries and 

 apex of primaries and the 9 on the upperside of primaries shows 

 faint traces of upper black spot; it is a further development of cas- 

 toria apparently differing from both this form and pallida in the re- 

 duction of the black spots in the 9 ; we propose the name pallidissima 

 for the race and figure the type $ and 9 from Provo, Utah (Fks 

 4, 5, 10). 



P. NELSONI Edw. 



This appears to us, after an examination of the type, to be nothing 

 but a northern form of occidentalis Reak. ; the maculation of the un- 

 derside of the secondaries is practically identical with that of the 

 spring form calyce Edw. and the gray-brown color emphasized by 

 Edwards in his description is largely due to the worn nature of the 

 single specimen from which the description was made. The only 

 marked point of distinction for nelsoni is the narrowness of the discal 

 black mark on the primaries and a small series from Alaska before 

 us shows considerable variation in this respect, some specimens hav- 

 ing the mark as broad as in calyce and others agreeing with the figure 

 of nelsoni (Butt. N. Am. II, Pieris I.). 



Euchloe creusa Dbldy. 



This species and its various forms are extremely difficult to 

 elucidate and it is impossible for us to satisfactorily establish at the 

 present moment whether we are dealing with several forms or races 

 of one species or several closely allied species. The misidentification 

 of the true creusa is responsible for a good deal of the confusion in 

 nomenclature ; the types of this species are in the British Museum and 

 were taken by Lord Derby in the Canadian Rocky Mts. ; they are 

 figured by Verity (Rhop. Pal. Vol. I, PI. 68, Figs. 8-10) and a recent 

 examination by ourselves confirms Verity's opinion that these are the 



