ORNITHOLOGICAL EXPLORATIONS. 199 



the case iu all plumages, both summer and winter, but show the following 

 coloration : 



The ground color is a delicate creamy yellow, becoming whitish to- 

 ward the tip of the interior feathers. The outer web has a series of 

 dusky spots, while the inner one is marbled rather coarsely with black- 

 ish, darker toward the base, where the feathers appears dusky with faint 

 light mottlings, while the tij) is without dark markings. 



Proceeding now to the comparison of L. ridgwayi with allied forms it 

 will be well to bear in mind that there are at least four different stages 

 which must be compared with corresponding stages of the other kinds. 

 It would not do to compare a preeestival L. ridgicayi with a postsesti- 

 val muta, or a female of the former with a male of rtipestris. It 

 is, however, on similar comparisons that the present most generally 

 adopted views concerning this interesting group of birds are based. It 

 may furthermore be remarked that we are not satisfied with the nega- 

 tive results furnished by the fact that we hardly can distinguish ptar- 

 migans in their white winter plumage.* ifor do we consider all the 

 rock-ptarmigans identical, even if the distinguishing marks pointed 

 out by the late Professor Sundevall do not hold good. He paid es- 

 pecial attention to the greater or lesser extent of the white markings 

 on the exterior tail-feathers, but later authors have denied the value of 

 this character and proved a great individual variation iu this resi)ect. 

 Nevertheless, it seems to me that the characters will average as indi- 

 cated by him. An observation by me, and verified oti a large series of 

 specimens, seems to prove, that the females have more white at the base 

 of the exterior rectrices than the males. 



It has already been mentioned that L. ridgwayi is sufiiciently distin- 

 guishable from L. rupestris by the uniform black prsepectus of its preses- 

 tival plumage, agreeing in this respect witii muta and its allies. From 

 these it is distinguished in its summer plumage not only by the saturated 

 brown color, but especially by lacking every trace of whitish or grayish 

 edgings of the feathers, there being in the postaestival plumage only 

 some faint indications of lighter rusty at the end of a few feathers. I 

 have seen Norwegian specimens of L. muta almost without whitish 

 edgings, but it was in every case plainly due to abrasion, while in the 



'This assertion does not seem quite superfluous in view of the following compari- 

 son of Dr. O. Finch : " One specimen [of alba'] iu the uniform white wiuter plumage 

 froui Alexaudrovsk is not in the least distinguishable from European specimens 

 (from Russia and Norway) in the muTseum iu Bremen. The distribution of the spe- 

 cies lalba] coDHeqtiently embraces the whole Arctic region, as is also the case with L, 

 alpinus NiLSS, 



