IO Chapman on Geothtyfis trickas ignota. [January 



western forms, the birds themselves are in a degree intermediate, 

 as Mr. Ridgway has already shown.* In the extent of the 

 yellow markings of the underparts, they approach occidental is ; 

 in the restriction and coloration of the ashy band bordering the 

 black facial mask, and in measurements, they agree with true 

 trichas. In order to express the approximate degree of relation- 

 ship they bear to each form, I have adopted the following method : 

 Selecting from the Mississippi Valley lot two series, each of five 

 specimens, representing respectively the extremes of coloration 

 of both upper and under surface with their connecting stages, I 

 have given to each stage a purely nominal, but relative, value. 

 Thus the most highlv colored specimen in either series I have 

 rated at five, the next at four, and so on. These representative 

 scries I have used as a standard of comparison for (i) a series of 

 true trie has from the Atlantic States, for (2) the Mississippi 

 Valley series, and for (3) a small but representative series of 

 occidentalism taken throughout its range. In the appended table I 

 present an average of the results obtained, including also the 

 average measurements of these specimens, all of which are adult 

 males in breeding plumage. 



Exposed Extent of 



Wing Tail Tarsus Oilmen Yellow Ashy border 



20 specimens 



from Atlantic States 2.20 2.04 .77 .42 2.65 3.33 



3S specimens 



from Mississippi Valley 2.20 2.02 .77 .42 3.73 3.36 



10 specimens 



of occidentalis 2.25 2.14 .77 .42 4.60 4.60 



An examination of this table shows how well it sustains the 

 previous conclusion that the Mississippi Valley birds, as a whole, 

 are nearer the eastern than the western form. Considering them 

 now individually, I find there is not a specimen in the series of 

 thirty-eight males which I cannot match in the series from the 

 Atlantic States, nor is there a specimen in this latter series which 

 does not find its counterpart among the birds from the Mississippi 

 Valley. In neither series do I find a specimen as highlv colored 

 as are the extreme examples of occidentalis. I think, therefore, 

 we may safely refer the Mississippi Valley bird to Geothlypis 

 trichas verus. 



♦Manual N.A. Birds, p. 523, foot-note. 



