UNOULATA. 335 



i. 1, c. 0, pm. 4, m. 3 



. The umxjr incisors are large chisel-shaped teeth 

 i. 1, c. 1, pru. 3, in. 3 



elongated autero-posteriorly ; while the lower incisors are pointed and 

 diminutive between the pair of large procumbent canines which meet the 

 upper incisors. The upper molars are scarcely complicated with crests 

 and crochets. Digit no. v on the manus is represented not only by its 

 metacarpal but also by two phalanges ; but it is comparatively small and 

 must have been almost functionless. The finest remains of Aceratherium 

 hitherto discovered are those from the Middle Miocene of Sansan and 

 other French localities, and from the Lower Pliocene of Eppelsheim, Hesse 

 Darmstadt. There are also traces of the genus in the Lower Pliocene of 

 Pikermi (Greece), the island of Samos, Maragha (Persia), the Siwalik Hills 

 (India), and in China; and detached teeth have been identified in the Red 

 Crag of Suffolk. The typical species is Aceratherium incisivum, with a 

 skull about half a metre in length, best known from Eppelsheim. Nearly 

 complete skeletons of very similar rhinoceroses are known both from the 

 Lower Miocene (White River Formation) and the Upper Miocene (Loup 

 Fork Series) of North America; and some of these (e.g. Aphelops) are 

 clearly destitute of a fourth digit in the manus. 



Diceratherium. One small American rhinoceros closely resembling 

 Aceratherium^ exhibits a slight eminence on each nasal bone, as if the 

 animal had been provided with a pair of callosities (scarcely true rhino- 

 cerotine horns) placed side by side. The nearly complete skeleton of 

 Diceratherium armatum, with four digits in the manus, is known from the 

 Middle Miocene (John Day Formation) of Oregon. In the Lower Miocene 

 of France and Germany there seem to be traces of a nearly similar animal 

 (the Rhinoceros minutus of Cuvier). 



Rhinoceros (fig. 193). Typical rhinoceroses with a well-developed 

 horn date back in Europe as far as the Middle Miocene of France 

 (Rhinoceros sansaniensis) ; and fine skulls of a similar form have been found 

 in the Lower Pliocene of Eppelsheim, Hesse Darmstadt (Rhinoceros 

 schleiermacheri). The horns, of course, are never preserved under the 

 ordinary circumstances of fossilizatiou ; but the bone is always roughened 

 where they are attached, and so their original presence or absence can be 

 determined. It appears from this criterion that the Miocene species just 

 mentioned possessed two horns, one behind the other; and as they are 

 likewise characterized by the presence of one pair of incisors above and 

 below and well-developed procumbent lower canines, they may be placed 

 in the same group (sub-genus Ceratorhinus) as the existing It. sumatrensi* 

 of Sumatra, Borneo, and certain parts of the adjoining Asiatic continent. 

 One-horned rhinoceroses are unknown among fossils, except in the Indian 

 region of which they are now characteristic (R. unicornis and R. sondn- 

 cus). R. sivalensis and R. palceindicus from the Lower Pliocene of the 

 Siwalik Hills, seem to be their ancestors. The two-horned rhinoceroses 

 in which the front teeth are quite rudimentary or wanting (sub-genus 



