THE SONORAN REGION. [CHAP. 



family in the UintatheriidcR. These were huge, somewhat ele- 

 phantine ungulates, with five short toes to each foot, long tusk- 

 like canine-teeth in the upper jaw, and the skull surmounted with 

 three pairs of large bony protuberances ; their molar teeth being a 

 specialised form of the Coryphodon type. They occur in the 

 middle division of the Bridger, or the one above the zone yielding 

 Coryphodon, and may accordingly have been the descendants of 

 that genus. These uintatheres appear to have been restricted to 

 the " Bad Lands " of the Sonoran region and adjacent districts of 

 the Transition zone. 



FlG. 82. EXTREMITY OF SKULL OF UintCltherium , TO SHOW UPPER TUSKS. 



Passing by certain other forms of less interest, attention may 

 be directed to a peculiar group of aberrant mammals forming 

 the Tillodontia, which appear to be mainly North American, and of 

 which the serial position cannot be precisely determined. They 

 are restricted to the Eocene, and seem to combine the characters 

 of the modern Ungulata, Rodentia, and Carnivora. In the genus 

 Anchippodus, forming the type of the family AnchippodontidcB, the 

 skull approximates to that of a bear, the cheek-teeth are of an 

 ungulate type, and there is a pair of large chisel-like incisors 

 (preceded by a small functionless upper pair) in each jaw, very 

 similar to those of the rodents and hyraces. A second family, 



