MUSEUM OF COMPARATIVE ZOOLOGY. 115 



Passing to the Plains proper, the faded aspect of all the birds is 

 strikingly noticeable, especially in the species that range across the 

 continent. The well-known " neglecta " type of Stumella ludoviciana, 

 the " Henryi " type of Chordeiles popetue, the " rufa " type of Eremo- 

 phlla alpestris, the " Cassinii " type of Peuccea cestivalis, the " Park- 

 manni " type of Troglodytes aedo?i, the " septentrionalis " type of 

 Parus atricapillus, are not only prevalent forms, but corresponding 

 pallid forms are equally marked in Coturniculus passerinus, Spizella 

 socialis, Falco sparverius, ^gialitis vociferus, and others ; these pallid 

 races prevailing throughout the arid plains to the westward. The 

 same tendency is manifest in the mountains of Colorado, where the 

 Sitta " pygmcea " forms a similar pale race of Sitta pusilla ; * Zono- 

 triclda leucophrys, through the greater amount of ashy white on the 

 lores, passes into Z. " Gambeli " / Geothlypis Macgilllvrayi permanently 

 retains white spots on the eyelids, which appear in G. Philadelphia 

 only in the young and in the females. Pipilo erythrophthalmus, through 

 an acquisition of white streaks on the back and wings, becomes P. 



more noticeably that of the hallux — than those from Massachusetts; and in those from 

 Eastern Kansas they are fully as large as in Florida specimens, while the "P. arcticus " 

 in Colorado has them still larger. On the Pacific coast the specimens from Oregon 

 have small claws, the size increasing southward to Lower California, where they be- 

 come excessively enlarged. This increase in the size of the claws to the southward I 

 have traced in several other genera, it corresponding with the increase in the size of 

 the bill in the warmer latitudes, and is doubtless due to a similar climatic cause. See 

 Bull. Mus. Comp. Zool., Vol. II, pp. 230, 239. 



* Sitta " pi/gnuEd" differs from S. pusilla in being everywhere lighter colored; the 

 head is greenish ashy brown instead of pale hair brown, the back is less deeply blue, 

 and the white markings on the tail and wings are broader and purer. In <S. pusilla the 

 middle tail-feathers are generally only slightly paler at their bases, but are sometimes 

 distinctly white, as they almost always are in S. pygmcea. The oblique white bar on the 

 other tail-feathers is also much broader and more strongly white in S. pygmcea. In S. 

 pusilla the edge of the wing is generally pale grayish white, but sometimes distinctly 

 white, as are also the basal portions of the inner webs of the greater primary coverts. 

 In S. pygmcea the white on the edge of the wing is not only more strongly marked, but 

 covers also a larger portion of the inner vanes of the greater primary coverts, and the 

 concealed basal portion of the primaries also shares the white. The outer edges of the 

 primaries are also more broadly bordered with white than those in S. pusilla. The style 

 of markings in the two forms is identical, only that the white is more pronounced and 

 the general tints paler in S. pygmaa than in S. pusilla, apparently establishing it as a 

 paler race of the latter, co-ordinate with so many other similar examples of pallid races 

 in the interior of the continent. 



In like manner the western race of Sitta carolinensis (S. aculeata Cass.) has less black 

 on the inner secondaries than has the eastern form of this species. 



