188 BULLETIN OF THE 



North America — the group Hylocichla of Professor Baird — may be 

 taken. Three of these species {Tardus fuscescens, T. Swainsoni, and 

 T. Pallasi) are so closely related that for many years they were vari- 

 ously confounded with each other by almost all who wrote of them, 

 one of them not being clearly recognized as distinct from the others till 

 thus established by Dr. T. M. Brewer,* in 184 1, and also at about the 

 same time by Mr. J. P. Giraud.f each apparently independently of the 

 other. Yet they are so distinct that there seems to be not the slightest 

 excuse for again confounding them. While they all agree so closely in 

 general size, in form, and in proportions, that a series of detailed meas- 

 urements of many specimens of each species gives in the average no 

 constant differences in any of these particulars, each differs from the 

 other radically and constantly in style of coloration, and somewhat in 

 general tints, in habitat, nidification, habits and song. Two of these 

 species (T. fuscescens and T. Swainsoni) agree in the style of the colora- 

 tion of the dorsal surface, but differ so much in the color of this part, that 

 this character alone is always sufficient to separate them, while a still 

 wider difference is seen in the color and markings of the ventral surface, 

 a glance at this part of T. fuscescens being sufficient to invariably dis- 

 tinguish it from either of its above-named allies. The third species (T. 

 Pallasi) differs markedly from both the other two in the style of color- 

 ation of the dorsal surface, the rump and tail being conspicuously dif- 

 ferent in color from the anterior part of the body, whilst the others 

 exhibit no contrast of color between these regions. But the under sur- 

 face of T. Swainsoni is so like that of T. Pallasi that frequently speci- 

 mens cannot readily be referred to the one species rather than to the 

 other from a view of this surface alone. This group serves as a fair 

 general illustration of the kind of variation in color usually seen in 

 closely allied species, but there occur occasional exceptions, where a 

 difference in the relative proportions of different parts, or a wide differ- 

 ence in size, is the prominent specific distinction, the smaller species, so 

 far as color is concerned, being a diminutive representative of the larger. 

 Taking the present group of Hylocichla (for reasons that will appear 

 hereafter]) as a group illustrative also of individual variation, it is found 

 that the differences in color in different individuals of either species 



* Proc. Boston Soc. Nat Hist, Vol. I, p. 191, July, 1844. 



t Bird of Long 1 land, p. 91, 1843-44. 



X See the remarks on these species in Tart IV. 



