MUSEUM OF COMPARATIVE ZOULOGY - . 231 



An increase in the length of the bill is most frequent in long-billed 

 species, while in short-billed ones the increase is in general size, without 

 material change in its proportions. With the increased length and 

 slenderness of the bill there is in many cases also a tendency to greater 

 curvature. 



An increase in the length of the bill is quite marked in the genera 

 Quiscalus, Agelceus, Geothlypis, Troglodytes, Seiurus, Harporhynchus, 

 Galeoscoptes, etc. Quiscalus purpureus and Agelceus phamiceus afford 

 good illustrations of geographical variation in the size and shape of the 

 bill. Notwithstanding that the northern specimens are the larger, the 

 southern ones have, in the average, bills as long, though slenderer, than 

 the northern, and occasionally even longer. These differences are shown 

 to some extent in Plates VI and VII, where the figures of the bills 

 of Massachusetts and Florida specimens of these species are given side 

 by side. In Plate VI, figures 1 and la represent the bill of an average 

 Massachusetts male A. phozniceus, and figures 2 and 2a the bill of an 

 average Florida male of the same species. The latter, while much less 

 thick, is fully as long as the former. Figures 4 and 4a represent the 

 shortest bill of a considerable series of Massachusetts specimens, and 

 figures 6 and Go the shortest or thickest bill of a similar series of Florida 

 specimens. Figures 3 and 3a give the longest bill of the Massachusetts 

 series, and figures 5 and ba the longest of the Florida series, the speci- 

 mens being in each case adult males. Plate VII, figures 3 and 3a rep- 

 resent the bill in average Massachusetts males of Quiscalus purpureus, 

 and figures 2 and 2a that of average Florida specimens, while figures 1 

 and la, and I and 4a, show respectively the longest and the shortest bills 

 of a considerable series of Massachusetts specimens. Figures 5 and ba 

 are from a New Jersey specimen, and figures 6 and 6a from a Florida 

 specimen, the latter showing an inflection of the upper mandible more 

 or less frequent in the various species of Quiscalus. The figures, as in 

 the previous plate, were all drawn from adult males. Jn each of these 

 species the average difference in the bills of Florida and Massachusetts 

 birds is as great as is frequently considered to be sufficient to constitute 

 specific differentiation, and between the extremes, especially of A. phoz- 

 niceus, even subgeneric. Yet specimens from intermediate localities 

 resent such a gradual and complete transition between the two forms 

 as to render their specific identity unquestionable. 



A similar difference between Massachusetts and Florida examples, 



