ARCHAEOHYRAX 61 
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-7ypotheria, though less 
specialized than the other families. 
Archaeohyrax Ameghino 
Archaeohyrax Amegh., 1897, Bol. Inst. 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 }74>. 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 
