COLLURIO. 449 



graduated. These differences are, however, most appreciable in 

 specimens from the middle and western provinces Those from the 

 Western States, east of the Missouri River, as far north as Wiscon- 

 sin, are more intermediate between the two, although still nearest to 

 the Rocky Mountain bird as described; the back darker, the rump 

 and axillars more plumbeous, the sides more bluish I have little 

 doubt that the examination of series from the States along the 

 Mississippi will show a still closer resemblance to typical C ludo- 

 vicianus, and that the gradation between the two extremes will be 

 found to be continuous and unbroken. It therefore becomes a 

 question whether there is really more than one species, varying with 

 ipngitude and region, according to the usual law, the more western 

 Wbe lighter, with longer tail ; or whether two species, originally dis- 

 tinct, have hybridized along the line of junction of their respective 

 provinces, as is certainly sometimes the case. The approximation 

 m many respects of coloration of the Shrikes of the Pacific coast to 

 those of the South Atlantic States, is not without its importance in 

 the discussion of the subject. Pending the decision of this question, 

 however, I propose to retain the name of excubitoroides, as repre- 

 senting, whether as species or variety, a peculiar regional form, 

 which must be kept distinctly in mind. The comparatively greater 

 size of the bill in the Cape St. Lucas specimens is seen in other 

 species from this locality. 



The intensity of the black front in this species varies considerably, 

 sometimes very distinct, and again entirely wanting. This may 

 probably be a character of the breeding season, the dulness of black 

 anterior to the eye, and the lighter color of the bill, having a close 

 relationship here, as in other species, to maturity, sex, and season. 



The essential differences betAvcen this species and the G. excubitor, 

 of Europe, Avill be found in the diagnosis given under the generic 

 head. They are quite appreciable on a slight comparison. 



Specimens examined, over one hundred in number. The more 

 important localities are the following : — 



29 June, 1866. 



