OVERLAPPING FORMS 



157 



bluish green, bronze green, or bronze purple. The details are 

 complicated and difficult to appreciate without actual specimens, 

 but the two common types are sufficiently distinct. The birds 

 inhabit the whole area east of the Rockies, guiscula aglaeus oc- 

 cupying Florida and the Southern States southwest of a band 

 of country about a hundred miles broad extending roughly from 

 Connecticut to the mouth of the Mississippi; and aeneus taking 

 the area north and west of this band. In discussing this case 

 Chapman expresses the same view as Allen does in the Colaptes 

 case, that there are two distinct populations, substantially fixed, 

 and that the band of country in which they meet each other 

 has a mongrel population, with no consistent type, but showing 

 miscellaneous combinations of the character of the two chief 

 types. 



The warblers of the genus Helminthophila provide another 

 illustration which has points of special interest. The two chief 

 species are H. pinus, which has a yellow mantle and lower parts, 

 white bars on the wings, a black patch behind the eyes and a 

 broad black mark on the throat ; and H. chrysoptera with dark grey 

 mantle and pale whitish grey lower parts, yellow bars on the 

 wings, and grey marks on cheeks and throat where pinus has 

 black. These two birds are exceeding distinct, and in addition 

 their songs are quite unlike. H. pinus ranges through the eastern 

 United States up to Connecticut and Iowa. H. chrysoptera is a 

 northern form extending down to Connecticut and New Jersey. 

 Both are migrants. 



In these two States, where the two types overlap, certain 

 forms have been repeatedly found which have been described as 

 two distinct species, Lawrencei and leucobronchialis. Dr. L. B. 

 Bishop and Mr. Brewster showed me two long series of Hel- 

 minthophila containing various intergrades between the four 

 named kinds, and details regarding these may be found in 

 Chapman's North American Warblers and in Dr. Bishop's paper 

 in Auk, 1905, XXII. Though the characters evidently break 

 up to some extent, the series can be represented as due to re- 

 combinations of definite factors more easily than the others 

 which I have described. The differentiating characters are: 



