402 LOWER VERTEBRATES. 



having twenty-nine. It is of a yellow color above, \vith the ordinary series of small 

 transverse rhombs, which send lateral prolongations to the sides of the body. It 

 inhabits Lower California. 



Crotalus tigris is a form which has the nasal plate divided, and the keeled scales 

 disposed in as many rows as those of C. cerastes. The head is depressed, and being 

 narrow behind, and the nose broad and obtuse, it is quite quadrangular in outline. 

 The animal is of a yellowish ash above, with small clustered blotches anteriorly, which 

 develop into brown bands further back. C. cerastes inhabits California, Arizona, and 



Mexico, preferring localities where there is absolute- 

 ly no trace of vegetation, such as are those of the 

 southwest deserts, where it is extremely abundant. 

 Its chief structural peculiarity is the pair of horns 

 surmounting the head, and giving the animal the 

 appearance of the horned-viper, Vipera cerastes, of 

 Fig. 232.— Head of Crotalus cerastes, Africa, which animal it further resembles in being 

 horned-rattler. ^^^.^ sluggish, and in its choice of locality. The 



New Mexicans h.ave named this animal the ' side-winder,' because of the slightly 

 lateral motion which they have in passing forwards. 



The next member with which we deal is C. pyrrhus which has the head obtuse and 

 rounded, the labials fourteen, and the loreals four. It is a most highly colored 

 animal, being of a bright salmon red, with transverse bars of a deeper shade, which 

 are broadest along the back, and lateral series of yellow blotches. A specimen cap- 

 tured in Arizona during a hasty retreat from hostile Indians, by members of the 

 'Wheeler Survey,' attracted considerable attention as a 'red rattle-snake.' C. 

 mitchellii has many points in common with the red-rattler, though it has but one 

 loreal, and the small upright nasal is separated from the rostral and labials by a series 

 of small scales. The general color is grayish 3-ellow, with indistinct quadrate mark- 

 ings along the back, which at the tail are reduced to bands. The scales are in twenty- 

 five rows. This animal, the last of the genus, has been only found in Lower Cali- 

 fornia. 



The last and highest member of the family Crotalidas is the Aploaspis lepida, a 

 form inhabiting western Texas, and first described in 1861. 



Oedee II. — PYTHONOMORPHA. 



The members of the order which we now treat lived at a time when the American 

 continent was considerably lower than it now is. New Jersey and Delaware, as 

 well as a greater portion of the southern states, wei-e then under water. The Mexican 

 Gulf extended as far north as the Ohio River, and the Rocky Mountains, in some 

 places 10,000 feet lower than they now are, appeared as a range separated from the 

 valley of the Mississippi by a broad expanse of salt water which teemed with animal 

 life ; the immense chalk-like deposits of the protozoans suggesting the name of the 

 period, the cretaceous. It was during this period, when the sea was somewhat warmer 

 than at present, that gigantic reptiles, in their general form and movements resembling 

 huge eels, ploughed through the water by means of their four paddles and propeller- 

 like tail, in search of fishes and other marhie life, much in the same manner as does 

 the searsnake of to-day. 



