771a Extinct American Rhinoceroses and their Allies. [ December, 
ON THE EXTINCT AMERICAN RHINOCEROSES AND 
THEIR ALLIES? 
BY. E: D.. COPE; 
WELVE species of mammals which may be called rhinoc- 
eroses, have been defined from materials obtained from the 
Tertiary formations of North America; and five additional spe- 
cies have been distinguished, which may be regarded as more or 
less nearly allied to that family. A few additional names have 
been proposed for supposed species whose characters are not yet 
established. In the corresponding formations of Europe and 
Asia, the fossil remains indicate a still larger number of species. 
The forms included in the family, first appear in both continents 
in the Lowest Miocene or Oligocene epochs ; that is, in North 
America in the White River formation. The family still exists in 
Asia and Africa, but in Europe it disappeared during the glacial 
epoch. In North America it became extinct at a still earlier 
period, no remains of rhinoceroses having been found in beds of 
later age than the Loup Fork, or Upper Miocene period. 
The genus Hyracedon (Leidy) which has a full series of incisor 
teeth, was formerly included in this family, and it agrees with the 
various genera in the structure of the molar teeth of both jaws. 
But I have ascertained that it differs so widely from them in some 
other respects, that it became necessary to regard it as the type 
of another family, the Hyracodontide. The mastoid bone forms 
part of the external wall of the skull as in tapirs, and the neck is 
quite elongate. It fact the Myracodon arcidens must have had 
the proportions of some of the horses in this respect. There is 
also no posterior tuberosity of the mandibular condyle, so con- 
spicuous in the rhinoceroses. 
The following table explains the relations of the two families: 
IV. Anterior exterior crescent of superior molars much reduced; inferior molars with 
cross-crests; superior molars and premolars alike, with cross-crests. 
6. Mastoid bone forming part of the external Ssi of the skull; no PAE 
of the mandible; neck elon racodontide 
7. Mastoid bone excluded from the walls of the skull by the penr of the 
occipital and squamosal; a postcotyloid tuberosity of the mandible; neck 
short .._ Rhinoceride, 
ee eee ener 
The genera of Riinoceride differ from each other as foilon : 
I. Four anterior digits. e 
ee canine 2; no horn; posttympanic bone distinct.....4ceratherium. 
ted oe pope eee in the Bulletin of the U. S. Geol. Surv. Tere 
ai 
