ARCHAEOHVRAX 6l 



whole Deseado fauna, we would seem to be dealing with 

 the inhabitants of an arid area, where bushes have, in part 

 at least, replaced the grass. The typotheres seem to me 

 to represent a part of the fauna which lived by gnawing 

 the bark and eating the twigs and leaves of bushes. This 

 does not preclude the eating of grass also, but I do not 

 see how they would have developed all their peculiarities 

 by eating grass alone. The rodents are of such insignifi- 

 cant size that they could hardly have monopolized this 

 food supply, and the typotheres seem to have adjusted 

 themselves to, and occupied the place of rabbits on our 

 western plains; but went even farther in developing in 

 great numbers and varieties. 



Systematic Descriptions 



Archaeohyracidae Ameghino 



This family is differentiated by the presence of enamel 

 on all sides of the first incisor, by the unreduced condition 

 of the lateral incisors, and by the small bulla of the mas- 

 toid. These are primitive features. Ameghino considered 

 this family to belong to the hyracoids; but, as explained 

 earlier, I believe them to be true Ty pother ia, though less 

 specialized than the other families. 



Archaeohyrax Ameghino 



Archaeohyrax Amegh., 1897, F*°'- I nst - Geog. Argen., t. 18, p. 431. 



This interesting genus is known by a complete skull 

 found by Ameghino and of which we found no duplicates. 

 I insert a reproduction of the side view of the skull, and 

 the dentition is shown in fig. 24 a, and fig. 25 a. The 

 dental formula is 3 | ^ 3 • Incisor 1 is a little larger than 

 the other incisors. Each upper molar has a vertical groove 

 near the anterior external margin. In each upper premolar 

 (after the first) and molar, there is a central pit surrounded 



