1894.] Vertebrate Fossils. 245 
and hornless forms of each continent may reasonably be con- 
sidered to have been developed independently from it. There 
seems at present no evidence for supposing that there was any 
interchange of species between the two continents later than 
early Miocene times. This degree of parallelism is all the 
more striking when we consider the length of the period of 
isolation in connection with the marked degree of similarity 
shown. This similarity is exhibited not only in the develop- 
ment of a nasal horn, but also in the general appearance of 
the skull, the complexity of the structure of the teeth and 
their arrangement in the jaw, and the relations of the post- 
tympanic and post-glenoid processes, Figs. I-4, Plate II, show 
the latter in the genera Rhinoceros, Teleoceras, Aphelops and 
Ceratorhinus. On the same plate, figs. 5, 6, 7, 8 & 9 represent 
various stages of tooth development from Aceratherium to 
Teleoceras and recent forms. As regards specialization of 
parts and complexity of tooth structure, from what is at pres- 
ent known of Teleoceras, it may be regarded as equalling in 
these respects any of our recent forms. If we compare it with 
Rhinoceros sansaniensis (Lartet) from a horizon in France of 
which our Loup Fork has been considered an equivalent, it 
will at once be seen thatthe tooth structure of the latter is 
much simpler and more like Aceratherium. See Plate II, fig. 
7 (after Filhol). If these beds be really of the same age we 
must conclude that the conditions favorable for the develop- 
ment of the more modern types of the Rhinoceride, existed 
to a much greater degree in America than in Europe, a condi- 
tion of affairs not improbable when we reflect that the family 
was originated on this continent. 
Technically, perhaps, Teleoceras should not be considered 
as generically distinguishable from Rhinoceros, and had it 
n found in Europe it would doubtless have been referred 
to that genus. Since however it is an American form, found 
in the same beds with Aphelops, its unmistakable ancestor, 
which latter as has been shown by Cope, Scott and Osborn, is 
quite distinct from Rhinoceros, I have decided to refer it to a 
distinct genus; believing that classification should rest so far 
as possible upon our knowledge of actual relations, and should 
