I poo.] Osborn, Phylogeny of the Rhinoceroses of Europe. 23 1 



phyla in North America, Europe, Asia, or Africa, and the sub- 

 sequent intermingling of these phyla by migration. 



(3) To recognize the succession of species in separate phyla 

 or lines of descent, designating them as subfamilies by the ter- 

 minal incB. 



(4) To sharply mark off each subfamily or phyletic series of 

 species from its contemporaries as soon as its earliest members 

 appear. 



(5) To anticipate within each phylum the probable develop- 

 ment of collateral as well as of direct lines of species, by the laws 

 of local adaptive radiation. 



Among the main divergent characters for the discrimination 

 between subfamilies or series of species are : 



1 . Proportions : 



a. Long-skulled (dolichocephalic), and long-footed (doli- 

 chopodal), or long-limbed types, e. g., Atelodus simus. 



b. Short-skulled (brachycephalic), short-footed (brachy- 

 podal), or short-limbed types, e.g.., Teleoceras fossiger. 



2. Reduction of digits : 



a. Precociously tridactyl types, e.g., C^nopus tridactylus. 



b. Persistently tetradactyl types, Aceratherium tetradac- 

 tylum. 



3. Developmefit of horns : 



a. In lateral pairs on nasals, e.g., Diceratherium pleuroceros. 



b. Single on nasals, a, on tips, e. g., Teleoceras, b, on centre, 

 e. g., Rhinoceros. 



c. In longitudinal pairs on nasals and frontals, e. g., 

 Ceratorhinus. 



d. Single on frontals, e. g., Aceratherium incisivum, Elas- 

 motherium. 



4. Cutting teeth : 



a. ' Megalodine types,' in which the cutting teeth persist, 

 <?. g., Rhinoceros indicus. 



b. ' Atelodine types,' in which they degenerate, e. g., 

 Atelodus simus. 



Some of these divergent characters also become convergent or 

 homoplastic and are employed to distinguish the generic and 



