Eaton — Vertebrate Fossils from Ayusbamba, Peru. 151 



parison, there is no doubt that it belongs under the genus 

 Parahipparion . 



Examination of an upper molar (text-figure 7) leads to about 

 the same conclusions as were obtained from the study of the 

 lower teeth already described. This tooth appears to be 

 either the first or the second upper molar of the right side. 

 Probably it is the first. The length is 21-5 mm and the width 

 22 mm . The depth of the crown is greatly reduced, only about 

 3Qmm f t ] ie p r j sm being left. In fact, it is so low as to present 

 an almost senile stage of wear. Under these circumstances not 

 only would the pattern of the enamel foldings be simplified, 



Fig. 5. 



Fig. 6. 



Fig. 7. 



Fig. 5. Pm 2 and Prn 3 , Parahipparion sp., Ayusbamba. xO" 

 Fig. 6. Pm«, Parahipparion sp., Ayusbamba. x 0"80. 

 Fig. 7. M 1 , Parahipparion sp., Ayusbamba. x - 80. 



as compared with the condition at four or five years of age, 

 but the antero-posterior diameter, or length, of the crown 

 would be considerably reduced. The width of the crown has 

 probably been a little reduced also, but judging from the very 

 slight convergence of the labial and lingual sides of the prism, 

 this transverse reduction is very small, probably not exceeding 

 l mm . Making due allowance for advanced stage of wear and 

 for individual variation, it is conceivable that the enamel pat- 

 tern of this tooth might have been derived from the pattern 

 exhibited by the first upper molar of any one of the species of 

 Parahipparion in which the true molars have been observed. 

 These teeth have not been observed in P. peruanum, the 

 species that from its occurrence at Tirapata would seem most 



