INTBODUCTOBY OBSEBVATIONS. 
American rhinoceroses. — Since the first part of this volume was written a memoir 
by Prof. Cope 1 has come under the writer’s notice, in which the conclusion is arrived 
at that none of the American hornless rhinoceroses should be referred to the 
European genus Aceratherium . 2 : they are now classed as follows , 3 viz. : — 
Genus I. : Peracebas, Cope. 
I. J, C. -J, Pm. I, M. Digits? 
Peraceras super ciliosus, Cope. 
,, malacorhinus , Cop e.= Aphelops malacorhinus , Cope. 
Genus II. : Aphelops, Cope. 
I. A C.§, Pm. I, M. f. Digits g. 
Aphelops meridianus (Leidy). 
,, megalodus , Cope. 
,, fossiger , Cope. 
Genus III. : Canopus, Cope. 
I. f, Cg, Pm. I, M. f. Digits g. 
Ccenopus mills, Cope. = Aceratherium mite , Cope. 
The European genus Aceratherium has the dental formula of Ccenopus or Aphelops , but 
the digits (in the type species) are-g. 
The present writer being strongly opposed to the great multiplication of genera, 
as tending to obliterate the affinities of animals, would prefer to unite the whole of 
these three new genera with Aceratherium ; giving them at the most sub-generic 
value. The differences in their dentition are not greater than those found in the 
existing rhinoceroses, which the writer likewise unites under one genus ; the terms 
Atelodus , Ceratorhinus, etc., being used, if at all, as of subgeneric value . 4 The 
1 “Amer. Nat.,” pp. 540-610. 
2 It appears to be the custom now to spell this name Aceratherium , in place of Aceratherium. 
3 The outer so-called lower incisor is probably a canine. 
4 Among both the tetralophodont and trilophodont mastodons there are some forms with a produced mandibular symphysis 
furnished with incisors, while in others the symphysis is short and edentulous. Both of these forms (belonging, be it 
remembered, to distinct subgeneric groups) would be quite as well entitled to generic distinction, as the various forms of American 
aoeratheres. If the writer were rewriting the first volume of this work, he would drop the names Siegodon, Loxodon, and 
Euelphas, and merely retain the generic name Elephas. He would also pursue much the same course with the Bovidce ; using 
the term Bos in its old Linnean sense. 
