26O2 



SCALED REPTILES 



is obvious; and that this is really the case is shown by the circumstance that at the 

 present day rattles with twenty rings are very seldom met with, since with the ad- 

 vance of cultivation it is only rarely that these noxious reptiles are suffered to at- 

 tain their full age. The body is thick, and, for poisonous snakes, somewhat long; 

 and the poison glands attain very large dimensions. 



Since the rattlesnakes are extremely variable in coloration, reliance 



Rattle- k as to a great extent to be placed on the arrangement of the shields 



snake covering the fore part of the head in the discrimination of the species. 



In the common rattlesnake (Crotalus durissus} of North America, the 



distinctive characteristic is the presence of only two pairs of large shields between 



COMMON RATTLESNAKE. 



(One-fourth natural size.) 



the large supraocular and rostral shields; these paired shields being separated by a 

 series of small ones in the middle line. Of these shields, behind the large triangu- 

 lar rostral comes the four-sided anterior pair, representing the anterior frontals, 

 while to each of the latter further back joins a larger oval shield which must be 

 regarded as a lateral remnant of the hinder frontal. The space between the two 

 last-named shields is occupied by a series of small shields, of which the front ones 

 are the largest; and between the supraocular shields commence the long keeled 

 scales covering the body, where they are arranged in from twenty-five to twenty- 

 seven longitudinal rows. The ground color of the upper surface is a dull grayish 

 brown, upon which are two rows of large, irregular spots, which may unite into 



