MUSEUM OF COMPARATIVE ZOOLOGY. 223 



or of either of the forms figured, or of any intermediate form, as exem- 

 plified by the specimens of this species in the collection of the Museum. 

 Figure 15 and 15a and 16 and IGa (same plate) are accurate repre- 

 sentations of the bills of two Massachusetts males of Dendrceca striata. 

 The differences between these specimens, though so great, are not 

 greater than occur in different cospecific examples of several other 

 species of this genus contained in the Museum. 



Massachusetts specimens of Certhi a familiar is differ even more in the 

 form of the bill than do the specimens above figured of either Troglody- 

 tes a'edon or Mniotilta varia. They also present a similar range of color 

 variation in the plumage, and one equally at variance with the variation 

 in the bill. 



Figures 19 and 19a, 20 and 20a (same plate), show how widely 

 two Florida specimens (both males) of Pyranga cestiva vary in respect 

 to the size of the bill, the specimens in question differing but little in 

 general size. If these figures are compared with the figures recently 

 published of the bills of certain supposed species of Pyranga'* they will 

 be found to vary more than some of the latter do, and indicate how un- 

 satisfactory the nature of species must be when based mainly upon dif- 

 ferences in the bill. Other cospe'cific specimens of Pyranga in the 

 Museum exhibit great difference in the size, form, and position of the 

 tooth-like processes of the upper mandible, and in the color of the bill, 

 — differences that have been regarded as specific characters. The 

 color of the bill in many species of birds, in fact, varies greatly in speci- 

 mens of the same species taken at the same season, and generally in 

 those taken at different seasons ; yet it is a character that has been re- 

 lied upon for the distinction of species. 



Figures 1 and la, 2 and 2a, 4 and 4a, and 5 and 5a, Plate V, illus- 

 trate variations in the bill in Massachusetts representatives of .2EgiotJtns 

 linarius. Figures 3 and 3a, and 5 and oa, are drawn from specimens from 

 Arctic America, the first being an original specimen of the jE. fuscescens 

 Coues ex auct., and the other a similar specimen of the JE. exilipes Coues. 

 Figures 7 and la to 10 and 10a, inclusive (same plate), represent varia- 

 tions of the bill in male specimens of Chrysomitris tristis, a species allied 

 to JE. linarius. It will be seen that the two series are nearly parallel in 

 respect to the amount and character of the variations in the bill. 

 Figures 11 and 11a and 12 and 12a indicate similar variations in an- 



* Proceed. Phil. Acad. Xat. Sci., June, 1869, pp. 130-133. 



