The Swifts 



one's head, when it dodges from one side of the trunk to the other 

 as the observer is trying to locate the reptile, keeping out of the 

 line of vision in the same fashion as a squirrel. Like many of the 

 swifts, these lizards often burrow in the sand at the bases of the 

 trees, to pass the night. In this habit they resemble the horned 

 lizards (Pbrynosoma'). The majority of captives, if kept in a 

 cage with a few inches of gravel, burrow just deep enough to cover 

 the back, beginning this operation as the afternoon sun leaves 

 their cage. 



Group B. We now arrive at the second group of the Spiny 

 Swifts. There is a single row of large, supraocular plates, with 

 a single internal border and two external borders of small scales. 

 The species are of fair or moderate size. 



Yarrow's Swift, Sceloporns yarrovii, (Cope), is one of the 

 handsomest of the genus. Above it is a dark, rich purple, or 

 bluish-black the sides and limbs distinctly bluish. Each of 

 the scales of the upper surface contains a pale greenish or yellow- 

 ish spot. There is a broad, black collar on the sides of the neck, 

 bordered by a pale hue. Behind this collar is a V-shaped band 

 of black, extending over the shoulders. The chin and sides 

 of the abdomen are blotched with blue. Dr. Stejneger explains 

 that specimens of this lizard, when sluggish, will assume an 

 almost blackish hue that is quite uniform. 



The species attains a length of 8 inches. The scales are 

 weakly keeled and not so bristling as with others of the genus. 



Distributions. Fairly abundant in the southern portions 

 of Arizona, whence it appears to range a short distance into 

 Mexico. It lives among rocks and takes refuge in fissures when 

 pursued. 



The Western Swift, Sceloporus biseriatus, (Hallowell). 

 This is the commonest and most widely distributed of the Western 

 species. It is of moderate size. The scales are proportionately 

 small, and the scalation, will, at a glance, appear considerably 

 finer and smoother than many other Scelopori. 



The usual ground colour is light, greenish-gray. There 

 are no indications of a collar. Across the back are two series 

 of distinct, narrow and wavy bars. These are blackish and 

 narrowly margined in the rear with a much paler hue than the 

 ground colour. The sides of the abdomen and chin of the males 

 are blue on very old specimens, blackish. 



