232 Bulletin American Museum of Natural History. [Vol. XIII, 



medifosselte 



postfossette 



, crista 



-pre/ossette 



specific stages of several distinct subfamilies or phyla. Thus 

 several ' megalodine ' types gradually pass into ' atelodine.' 



Correlated with the above 

 fundamental divergent 

 characters are numerous 

 minor characters which 

 are of great service ; for 

 example, dolichocephalic 

 and brachycephalic Rhi- 

 noceroses frequently ex- 

 hibit also distinctive types 

 of auditory meatus, of 

 occiput, of premolar and 

 molar teeth, and of limbs. 

 An early division is ob- 

 served into heavier and 

 lighter types, correlated 

 with speed ; while collateral brachyodont (shrub-eating) and hypso- 

 </<?«/■ (browsing) species may arise within the same phylum ; example, 

 A. sifnus and ^. bicornis. 



Fig. I. 

 minology 



crochet 

 Typical Rhinoceros molar, showing ter- 



Family RHINOCEROTID^. 



Oligocene phyla. — Two similar lines appear simultaneously in 

 the Oligocene of Europe ; the most precocious of these is the 

 subfamily Diceratheriinae, represented in Europe and America ; 

 the less precocious is the Aceratheriinae, probably represented in 

 both countries also. The characters of both are sharply defined. 

 It is probable but not yet demonstrated that the smaller Rhinoc- 

 eroses throughout the Oligocene chiefly represent the Diceratheri- 

 inae ; nevertheless it is best to leave certain species incertcz sedis 

 {^R. velaunum, R. gaudryi), one or both of which may belong to 

 the Amynodontidae. 



Subfamily DICERATHERIIN^. PHYLUM I. 



Smaller Oligocene Rhinoceroses ; dolichocephalic, with paired nasal horns, 

 full-sized cutting teeth ; cursorial, long-limbed, with relatively slender bodies 

 well raised from the ground. 



General characters. — I. Manus precociously tridactyl (as observed in Ameri- 

 can species), correlated with swift motion. 2. Horns developed in lateral pairs 



