The Swifts 



complete — extending only about two-thirds around the crescent- 

 shaped margin — tiie rear supraoculars being in contact with the 

 larger plates of the head. There is a single outer margin of 

 small scales. The colouration of the members of this group is 

 in no way characteristic. 



Clark's Swift, Sceloporus clarkii, (Baird & Girard), is a 

 fine species, with large, sharply pointed, bristling scales. It 

 is rather characteristic from the large and very regular scala- 

 tion of the head, the shields being so sharply outlined that 

 the scale formula may be noted by the novice without the least 

 difficulty. 



Each body scale contains a greenish or bluish patch and is 

 usually edged with gray. The spots within the scales vary 

 greatly in intensity according to the activity of the individual. 

 If the lizard is active the greenish spots assume such decided 

 hues that the entire body appears to be of a greenish or bluish 

 tinge. If it is sluggish, the gray edges of the scales suffuse the 

 brighter colours and the prevailing hue is dull gray. On some 

 specimens there is a series of dull, wavy cross-bars of a dark 

 hue on the back; others have no trace of these, but on all there 

 are indications of a broad, black collar on the sides of the neck; 

 this is not margined with a lighter colour, nor is it visible from 

 above. The under-side of male specimens is dull white, with a 

 patch of vivid blue on each side of the abdomen and a similar 

 patch on the chin. 



Dimensions. — Following are the measurements of a speci- 

 men taken near Tucson, Arizona: 



Total Length 9 inches. 



Length of Tail 5 " 



Width of Body ... i^ " 



Width of Head 1 



Distribution. — Inhabits the deserts and sub-arid regions 

 of the southwestern United States. It occurs in southern Cali- 

 fornia and in Arizona generally, New Mexico, southern Nevada, 

 southwest Utah and northern Mexico. 



Habits. — Although an abundant lizard, it is difficult to cap- 

 ture. It skims over the desert soil if pursued, and, if decid- 

 ing to stop for a moment to reconnoitre, will actually slide a 

 few inches from the great momentum of its scampering pace. 

 If near a "pole" cactus or a yucca tree, it darts upward at a 



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