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 #xillars more plumbeous, the sides more bluish I have Jittle 
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 
longitude and region, according to the usual law, the more western 
the 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 
in 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 im 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 between this species and the C. excubitor, 
of Europe, will 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. 
