4-8. CROTALUS 957 



right out in the noonday sunshine of mid-summer. In 

 neither case were the snakes easily seen, as they were of the 

 exact color of their sandy surroundings. Both, though alert 

 allowed themselves to be noosed without moving away or 

 doing more than rattle feebly. 



Specimens which I have seen had eaten lizards, Uta 

 stamburiana, Cnemido-phorus tigris and Phrynosoma -platy- 

 rhinos. The Phrynosoma had been only partially swallowed} 

 and its horns had penetrated and protruded from the ventral 

 surface of the snake's neck. 



Regarding the mode of progression of this species Mr. 

 Cowles notes: "These snakes seem to be almost entirely 

 restricted to the sandy areas of the desert, rarely wandering 

 from them, and then only for a short distance, its mode of 

 locomotion admirably fits it for the type of country which it 

 inhabits. The ordinary snake finds difficulty in rapid motion 

 over the loose and shifting sand, since part of the tractive 

 power comes from a bracing of each loop of the body against 

 that part of the ground which is posterior to the loop, and 

 through the movement of the central portion of the body 

 against the surface of the ground. It can readily be seen 

 that a shifting and loose surface would seriously hinder the 

 progress of the ordinary snake. The "Side-winder," Crota- 

 lus cerastes, instead of progressing as do ordinary snakes, 

 longitudinally, progresses laterally, leaving separate tracks, 

 each paralleling the other, and angling in the direction in 

 which the snake is moving. Each track is approximately the 

 length of the snake making it, and is wavy, that is a series 

 of "S" shaped loops. The tracks give no sign of any part 

 of the body moving from one mark to the other, which gives 

 the impression that the snake jumps the three to six inch inter- 

 val between the tracks. Such is not the case, however. When 

 the snake is moving, the body is kept partially looped and 

 the advance seems to be through the advancing of the head 



