110 BULLETIN 114, UNITED STATES NATIONAL MUSEUM. 



lution, resulting from radiate migration, has perfected the marks in 

 central Texas and in Arizona; farther migration has resulted in 

 further change in these bars by which they lose their simple form and 

 become modified in two different ways independently — in the west 

 becoming broadened, in the east more or less broken into spots, and 

 bent, or curved. We see then, in these prefrontal and internasal 

 bars, their inception, perfection, and diverse modification. 



These white bars are not the only parts of the head pattern requir- 

 ing mention. White markings, spots, and bars of various shapes, 

 are considerably developed in all forms of the group except yuTnensiSj 

 the Great Basin section of hoylii, and splendida. The first two are 

 alike with white markings symmetrical, clean-cut, and limited to 

 the snout and sides. In splendida, in the central portions of its range, 

 the only white markings present occupy the same positions as in 

 yumensis, but are milch more restricted; the rest of the head is 

 black. In the western portion of its range these markings attain 

 the same development that they show in yumensis; in the eastern 

 portion it develops the markings of holbrooki. It is not necessary 

 to explain the variations of these markings in further detail; the 

 case is the same as with the prefrontal white bars; in splendida we 

 have the inception of two diverging lines of head markings, the east 

 and the west. 



One other portion of the head pattern may be mentioned. In all the 

 forms west of splendida the labials are white with narrow dark mutual 

 borders, except for the suture between the third and fourth upper 

 labials, the dark mutual border of which is so much widened as to 

 form a conspicuous circular spot or blotch on the upper lip beneath 

 the eye. In all the forms east of splendida the labials are light with 

 dark mutual borders, but there is no widening of the mutual dark 

 border of the third and fourth supralabials. Only as an occasional 

 individual variation is there any increase in pigment on the upper 

 labials beneath the eye — a variation as uncommon as the occasional 

 great reduction of the subocular spot in the west coast forms. Con- 

 necting these two divergent sections of the group we have splendidaj 

 in the New Mexican portion of its range, with an almost totally black 

 head, its labials lightened only by a median narrow white bar on 

 each scute which often is not even continuous across its middle. 

 The condition in the other forms of the group has undoubtedly been 

 produced by a widening of these narrow median white bars; while 

 eastward they all widened, westward the dark pigment was retained 

 on the upper series beneath the eye. This seems to be the only 

 logical explanation of the peculiar distribution of this subocular 

 dark patch. 



Perhaps of even greater value is the evidence from the body pattern. 

 Here the diversity is apparently much greater. If we except cali- 

 fomiae (its relationship to hoylii has been sufficiently discussed, along 



