1868.] DAWKINS — EHINOCEROS ETRUSCUS. 215 



hj'psodont dentition reaches a maximum of development in the R. 

 tichorhinas, R. platj/rhinus, and R. simus. To the second or bra- 

 chydont* division belong Rhinoceros Etruscus and all the Miocene 

 species both of Europe and North America, the only exception 

 being presented by those from the deposit in the Sivalik hills, which 

 seems to me by ho means of indisputable Miocene age. Into this 

 group also falls the remarkable hornless Rhinoceros, the Acerothe- 

 rimn incisivum. This form of tooth, so universal in Miocene times, 

 is preserved now only in the deciduous teeth of the recent and fossil 

 species. We have therefore to compare Rhinoceros Etruscus with 

 Miocene rather than Pliocene or Pleistocene members of the genus ; 

 and so closely does it approach some of these that an isolated tooth 

 could hardly be determined with absolute certainty if the locality 

 were unknown. All its characteristics occur in an intensilied form, 

 but are not altered in any essential point. It differs from the Rhi- 

 noceros of Auvergne only by the greater complexity of the anterior 

 valley, by the larger development of the posterior combing-plate, and 

 by the more slightly defined guard on the inner aspect of the pre- 

 molar series. In the latter species, however, the first premolar, 

 pm. 1, is persistent, so that it presented the normal molar formula 

 of the placental mammals. The exact geological horizon of this 

 species is very obscure. It was derived, according to M. Gervais't, 

 from the "pseudo-pliocene d'lssoire," and is the same as the R. 

 elatus of the Abbe Croizet, and has even been referred to the R. me- 

 garhinus of M. de Christol. The Rhinoceros hrachijpus, Lartet, from 

 the Miocene of Ville- Tranche d'Astarac, in Auvergne, has also four 

 persistent premolars. It diverges from the Etruscan species in the 

 following points : — The guard on the inner surface of the true molars, 

 which is merely sketched out in R. Etruscus, is fully and strongly 

 developed ; the strongly impressed guard in the premolars on the 

 posterior area, and in the true molars on both areas ; the posterior 

 combing-plate is not so strongly marked. The crowns of the 

 premolars are worn flat, while those of the true molars are ex- 

 cavated ; but this may possibly be a mere peculiarity of the indi- 

 vidual. In the lower molars of the same animal the guard is far 

 more strongly impressed on both areas, and especially so in the pre- 

 molars, and is veiy pronounced on the inner aspect of the anterior 

 coUis, which it traverses diagonally. The dentition of R. Simor- 

 rensis, Lartet, from the same locality as the last, presents the fol- 

 lowing points of difference: — In the upper jaw the guard is more 

 strongly impressed on the true molars, more slightly on the pre- 

 molars. The loAver jaws, however, of the two animals are identical 

 in form. Premolar 1 is present in both, being ver}^ small rela- 

 tively to the other teeth, and a mere representative of a departing 

 structure. All the teeth are very much smaller. The Rhinoceros 

 Etruscus is more or less allied to all these in the form of its teeth : 

 but its closest ally is the hornless Rhinoceros of Darmstadt, the 

 Acerotherium incisivum of Kaup (= R. incisivus, Cuvier). The latter, 

 however, is defined by the large incisors and by the persistence of 

 * ^paxvs = iihovt, o(ioi)§ = tooth. t Paleontologie, p. 59. 



VOL. XXTV. PART I. R 



