FOSSIL VERTEBRATES— MAMMALIA 833 
roses, has given perhaps the best summary of the position of 
these forms, -Hie says: {* The Perissodactyla may be primarily 
divided by the fundamental pattern of their upper grinding teeth 
into four superfamilies, as follows : 
1. TITANOTHEROIDAE: including the single family (1) Titano- 
theride. 
2. HippoipDEA: including the two families (2) Eguid@ and 
(3) Paleotheride. 
3. TaprIRoIpDEA : including the two families (4) Tapiride and 
(5) Lophiodontide. 
4. RHINOCEROTOIDEA : including the three families (6) Hyra- 
codontide, (7) Amynodontide, and (8) Rhinocerotide. 
To these should be added: 
5. CHALICOTHEROIDEA, an aberrant superfamily, with molar 
teeth related to the Titanothere pattern, and perissodactyl feet 
provided secondarily with claws. 
The eight families, in the order named, may be imagined 
as the contemporary branches of the four superfamilies, these 
in turn having branches from a still unknown Perissodactyl stem 
form — probably a Cretaceous member of the Condylarthra. 
These eight families, familiarly known as the Titanotheres, 
Horses, Paleotheres, Tapirs, Lophiodonts, Hyracodonts, Amyno- 
donts, and Rhinoceroses, when regarded as a series, present upon 
the one side close resemblances, or perhaps affinities, to the 
Artiodactyla, and an extreme departure from the Artiodactyla 
on the other. Thus the Titanothers exhibit many resemblances 
to the Artiodactyls, while the Rhinoceroses exhibit none at all, 
and are in many respects the most typical Perissodactyls. 
Superfamily RHINOCEROTOIDEA, or Rhinocerotine group. The 
three distinct families included in this division may be popularly 
known as the Cursorial or Upland Rhinoceroses, the Aquatic 
Rhinoceroses, and the True or Lowland Rhinoceroses. They 
are briefly distinguished as follows: 
Flyracodontide: cursorial rhinoceroses ; Hyrachyus and Hyra- 
codon; manus functionally tridactyl ; upper and lower incisors 
and canines persistent and uniformly developed. 
