TEIIl) LIZARDS OF THK GKNTS CNEMIDOPHORUS 155 



the desert floor of the Great Basin and of certain low-lying islands 

 in the Gulf of California. Here there is usually sand in abundance 

 and the sand itself is the chief protection of the species. Here the 

 burroAving habit, or the habit of running into the numerous small 

 holes in the sand, especially at the foot of bushes, is usually well de- 

 veloped. In this environment it is an advantage to have a coloration 

 like the sand, reddish or brownish, and one that is as near unicolor 

 as jjossible. Without going into a scientific explanation for the rea- 

 son for such a development, it may be stated that such a coloration 

 has actually developed in tlic sandy areas. Tiiis appears to have 

 been accomplished by the gradual dissolution, diffusion and concen- 

 tration of dark i)igment from the dorsal to tlie ventral surfaces, 

 where it is found on the throat, cliest. and abdomen. This results 

 in the blending of the dark and light reticulations of the back into 

 a dull, although still tessellateil. pattern. In some instances the 

 light longitmliual dorsal lines, wliich arc usually four in number 

 in the young and often in the adult of both sections, become nudti- 

 plied into many lines here, ami in other cases the populations tend 

 to become spotted, rather than leticulated. Still another modifica- 

 tion lies in the fact tliat specimens, especially in the south part of the 

 range, may lose almost all traces of longitudinal arrangement of the 

 dorsal markings, thus approaching the group of species which have 

 been described from the Gulf of California as nuD'fijris^ canus, haea- 

 tus, and cafalhiens/s. As will be seen in tracing these tendencies, 

 it appears that none of them is confined to a distinct, continuous, 

 geograi)hical area, so the splitting ofi' of subspecies seems out of the 

 question. 



The second series inhabits the higher levels, particularly the foot- 

 hills of the mountainous districts of the west (Oregon, California 

 and Lower California) and the same situations in the east (Western 

 Colorado, Texas, and Chihuahua). Here sand is usually replaced 

 by gravel, or even rocks, and either the rocks or simph^ brush be- 

 come the chief protection of the species. Here the burrowing habit 

 may be rendered impossible of development, and since the holes in 

 the soil are usually fewer, the species is often forced to take refuge 

 under rocks or brush when in danger, or to depend upon its swift- 

 ness and "protective coloration'' to deliver it from its enemies. In 

 tliis environment it is no doubt an advantage to have a broken, 

 sharply contrasting ])attern to give the impressicm of light and 

 shade beneath the sln-ubliery or of some lifeless debris upon the 

 ground. Since the color of the sui'i'oundings is dai'k, and not 

 reddish oi' bi'ownish a^ in the desert, a dark ground color for con- 

 cealment is clearly an advantage. The coloration of these lizards 

 thus appears to l)e an adajitation to the environmental conditions of 

 this habitat. This coloration appears to be due to a localization 



