322 ELEMENTARY ZOOLOGY 



which instead of being entirely molted as the rest of the 

 skin is, are, because of their peculiar shape, loosely attached 

 to one another, and by the basal one to the body of the 

 snake. The number of rattles does not correspond to the 

 snake's years for several reasons, partly because more 

 than one rattle can be added to the tail in a year, and 

 especially because rattles are easily and often broken off. 

 As many as thirty rattles have been found on one snake. 

 There are two species of ground-rattlesnakes or massa- 



FlG. 129. The gopher-snake. Pituophis bellona. ^Photograph from life 



by J. O. Snyder.) 



saugas (Sistrurns) in the United States and ten species of 

 the true rattlesnakes (Crotalus). The centre of distribu- 

 tion of the rattlesnakes is the dry tablelands of the south- 

 west in New Mexico, Arizona, and Texas. But there are 

 few localities in the United States outside the high moun- 

 tains in which "rattlers " do not occur or did not occur 

 before they were exterminated by man. The copperhead 

 (Agkistrodon contortix) is light chestnut in color, with 

 inverted Y-shaped darker blotches on the sides, and 



