246 CALIFORNIA ACADEMY OF SCIENCES. 



Central America. This latter form is distinguished by 

 the presence of a white spot above the eye, which is 

 wanting in the coast races. It is difficult to understand 

 how climate could have produced this marking, and it 

 seems more proper to regard it as a discriminative char- 

 acter. Toward the north the ranges of the two forms 

 come together, and specimens from this region are in- 

 termediate in character. The farther we get away from 

 this neutral ground the more distinctly marked do the 

 characters become, showing the part isolation must play 

 in the matter. Toward the south the white spot becomes 

 successively larger and more distinct, until it reaches 

 its maximum at the southern limit of the species. It is 

 a remarkable fact that this bird is increasing the extent 

 of white in the very region in which Spinus psaltria is 

 growing melanistic. Furthermore, the eastern represent- 

 ative of the genus, C. frontalis, has the amount of white 

 reduced toward the south, as would be expected. It 

 seems inconsistent to maintain that the increase in the 

 white spot of G. steUeri toward the south can be due to 

 the same climatic influence which generally tends to in- 

 tensify the plumage, and I think some other explana- 

 tion must be sought. From the map it will be seen that 

 the interior and coast forms intergrade only at their 

 northern limit, and here the distinctive white marking 

 probably originated before the species spread to the 

 south. As it extended southward, it would become suc- 

 cessively farther and farther separated from the coast 

 form, and, like the land mollusks of the Hawaiian 

 Islands, would become more and more modified, with- 

 out regard to climatic influence. There are other 

 changes taking place in these two forms besides the 

 transformation of the white spot. The northern forms, 

 both coast and interior, are darker, with more of black 

 and brown, while the tendency toward the south is to 



