TEETH UNEARTHED AT OEESTON, ENG. 107 



bilobed posterior termination of the grinding surface 

 of the last upper molar, more closely approximates to 

 the extinct horse of the Miocene period, which Herr 

 von Meyer has characterized under the name of Equus 

 caballus primigenius. The Oreston fossil teeth differ, 

 however, from this in the form of the fifth or internal 

 prism of dentine in the upper molars, and in its con- 

 tinuation with the anterior lobe of the teeth, the fifth 

 prism being oval and insulated in the Equus primi- 

 genius of Von Meyer. 



" The Oreston fossil teeth, which in their principal 

 characters manifest so close a relationship with the 

 Miocene Equus primigenius, differ, like the later drift 

 species (Eq. fossilis], from the recent horse in a greater 

 proportional antero-posterior diameter of the crown, 

 and also in a less produced anterior angle of the first 

 premolar. I have named this British fossil horse 

 Equus plicidens. The fossil horse (Eq. curvidens) of 

 South America, which coexisted with the megathe- 

 rium,f and, like it, became extinct apparently before 



the more ancient pri mi genial species (Hippotheria) of the conti- 

 nental Miocene deposits, without being reminded of the peculiar 

 character of the enamel of the molars of the Elasmotherium, in 

 which it is folded in elegant festoons. This extinct pachyderm, 

 which surpassed the rhinoceros in size, resembled that genus 

 very closely in the general disposition of the folds of enamel in 

 the grinding teeth, but agreed with the modern horse in the 

 deep implantation of those teeth by an undivided base. The 

 Elasmothere appears, therefore, to have formed one of the links, 

 now lost, which connected the horse with the rhinoceros ; and 

 it is interesting to observe that some of the extinct species of 

 horse, in the analogous complexity of the enamel folds, more 

 closely resembled the Elasmothere than do the present species." 



f " The teeth of this most gigantic of the extinct quadrupeds 

 of the sloth tribe are small in proportion to the size of the ani- 



