An unusually perfect skeleton of an alligator discovered by Mr. H. F. Wells some years ago 

 in the Tertiary formation of the Big Bad Lands in South Dakota and only recently extracted at the 

 American Museum from the rock in which it had lain imbedded so many thousands of years. Alligators 

 are found at present only in .southern United States, Mexico, and China, Very little has hitherto been 

 known as to their geological history. This is a rather small specimen, probably not full grown. The 

 lower jaw measures 9'^A inches in length 



A Tertiary Alligator 



CROCODILES have narrow and tri- 

 angular skulls with a notch on each 

 side into which fits the large fourth 

 tooth of the lower jaw. In the alligators 

 and caymans the head is broailer and flatter 

 and the notch is lacking, the lower tusk fit- 

 ting into a socket in the upper jaw. Croco- 



diles are found in nearly all tropical coun- 

 tries, but alligators only in the southern 

 United States, Mexico, and China, and cay- 

 mans in South and Central America. 



Numerous fossil crocodiles have been 

 found in the Tertiary and older formations 

 of various parts of the world, but hitherto 



505 



