8. CALLISAURUS 161 



whether intergradation occurs. Miss Atsatt records an in- 

 dividual of C. V. ventralis which was very light on the white 

 sand at Whitewater, but developed a gray pattern on com- 

 ing under the shade of a scraggly bush. It may well be 

 doubted if the darker coloring of specimens from Pyramid 

 Lake is more than a similar reaction to their environment. 

 The specimens of C. v. myurus, however, do seem to have 

 an average reduction in the length of tail and number of 

 femoral pores. 



Habits. — Dr. Merriam states (N. Amer. Fauna, No. 7, 

 1893, p. 171) that the Gridiron-tailed Lizard "inhabits the 

 open deserts and runs with great swiftness over the sand 

 and gravel beds, carrying its tail curled over its back as if 

 afraid to let it touch the hot surface of the earth. It starts 

 off at full speed as if fired from a cannon, and stops with 

 equal suddenness, thus escaping or eluding its enemies, the 

 coyotes, hawks, and larger lizards. When running it moves 

 fo swiftly that the eye has difficulty in following, and when 

 at rest its colors harmonize so well with those of the desert 

 that it can hardly be seen. This species feeds on insects 

 and the blossoms and leaves of plants in about equal pro- 

 portion." 



Dr. Ruthven writes: "Owing to their light color, in- 

 dividuals so closely resemble the sand that they are rarely 

 seen until they run. The method of running is grotesque 

 but highly effective in covering ground. With the knees 

 and elbows well elvated, the body about on a plane with 

 them, and the tail curled over its back as if, says Dr. 

 Merriam, 'afraid to let it touch the hot surface of the 

 earth,' it dashes off across the sand so rapidly that it can 

 scarcely be followed with the eye, and stops in plain view 

 with a suddenness and apparent ease that is astonishing in 

 view of the speed with which it is moving. When at rest 



