INTRODUCTION. 



they apparently belong to existing species, the beds at La Combette, 

 near Champeix (page 97), and those at Tour-de-Boulade, Puy-de- 

 Dome (Part I. p. 126), are provisionally referred to the Pleistocene, 

 but they may be equivalent to the Upper Pliocene of Peyrolles, with 

 which they were associated by P. Gervais. 



Generic terms have been employed in a wider sense than is the 

 case with many contemporary writers ; and I am permitted to say 

 that my views in this respect are in the main those of Professor 

 Flower. Thus a difference of one or more premolar teeth, or in the 

 number of the digits, in allied forms has not been considered a bar 

 to generic unity ; and accordingly the genus Eurytherium has been 

 included in Anoplotherium (p. 188), while analogous instances will 

 occur in Part III. in the case of the Rhinocerotidce and Equidce. 

 Occasionally a genus (e. g. Eporeodon, p. 208)has been admitted which 

 appears to be founded upon somewhat insufficient characters. 



A few words may be advisable in regard to the specific identi- 

 fication of specimens from the Tertiaries of Prance and Germany, the 

 most noticeable instance being that of the German Palceomeryx medius 

 with the French Amphitragulus boulangeri and A. pomeli (p. 130). 

 In the majority of such instances the identification has been guarded 

 by a provisional reservation ; but as the specimens in the Museum 

 apparently present no distinctive points of difference, the only logical 

 course in each instance has been to include all of them under one 

 specific heading. Different views are entertained by different 

 writers as to the amount of variation in size which should be 

 regarded as of individual or of racial value. In the case mentioned 

 above Prof. Riitimeyer takes larger limits than Dr. Filhol, the 

 distinction between A. boulangeri and A. pomeli having been made 

 by the latter writer on small differences in the size and proportions 

 of the teeth of the lower jaw, all of which come well within the 

 limits allowed by Prof. Riitimeyer to Palceomeryx medius. The 

 latter writer has already identified French specimens from the 

 Middle Miocene of Isere with the German form ; and as the latter 

 occurs in the Lower Miocene of Weissenau, near Mayence, it is 

 primd facie highly probable that it should be identical with the 

 Lower-Miocene form of Allier. The probable respective identity 

 of the German Hyotherium meissneri and H. sosmmeringi with the 

 French Palaochcerus typus (Hyotherium ti/pum, p. 254) and P. major 1 , 

 together with that of the German Microtherium renggeri with the 



1 Vide Wilckens, Biol. Centralblatt, vol. v. p. 236 (1885). 



