238 BULLETIN OF THE 



similar to, but hardly so great as, that between the Atlantic and Pacific 

 coast examples of indentical species is likewise seen, the American 

 being in general several shades darker than the European. In certain 

 cases there is also a difference in the markings, as in some of the hawks, 

 in which in the European the transverse bars are broader and better 

 defined, and the longitudinal ones less so than in the American. This 

 is illustrated in Astur palumbarius and A, alricapiUus, in Acci'piter 

 nisits and Ac. fuscus, etc. In many instances the only tangible differ- 

 ences between so-called representative American and European species 

 consists in the darker, brighter, or intenser color of the American, the 

 differences being oftentimes less than that between specimens of the same 

 species from the Atlantic States and the Mississippi valley, or between 

 those from the Mississippi valley and the Pacific coast. Not unfre- 

 quently, however, are American and European specimens so nearly 

 alike, even of species that have rarely been considered as identical, that 

 without a knowledge of the locality whence they came it would be 

 impossible to confidently refer them to the one species rather than to 

 the other. 



There are also indications of various local differences in color in speci- 

 mens specifically identical within the larger areas above considered, 

 and which are in a measure exceptional to the general law of a west- 

 ward increase in color. The data at hand are at present too few either 

 to limit these exceptional areas or to indicate to what extent they are 

 exceptional. They appear, however, to be coincident with peculiar 

 climatic conditions, the exact nature and extent of which are likewise 

 imperfectly known.* 



Variation in the Length of the Tail and in other Characters. — At 

 certain localities, and more especially to the southward, there are well- 

 known instances of an increase in the length of the tail, without an ap- 

 preciable modification of other parts. Marked examples of this are 

 seen in Icteria virens, Harporhynchus rufus, and Mi/nus polyglottus, 

 as has h^en pointed out by Professor Baird and other writers,! each of 

 which species has a western long-tailed variety. The Quiscalus 

 macrura is also little else than a long-tailed variety of Q. major. A 

 tendency is seen to this variation in Geothlypis trichas at the southward, 



* See on this point below, p. 239 et seq. 



t See especially Prof. Baird in Amer. Joum. of Science and Arts, 2d Series, VoL 

 XLI, p. 191. 



