152 Eaton — Vertebrate Fossils from Ayusbamba, Peru. 



likely to be found in Pleistocene formations at Ayusbamba. 

 On the whole it appears that very little progress toward the 

 specific identification of the upper molar of text-figure 7 is to 

 be made through the study of its enamel pattern alone. Much 

 better results can be obtained by comparing its dimensions with 

 those of the various species of Parahipparion. Accordingly 

 the length and width of the upper true molars of P. saldiasi, 

 P. bolivianum, and P. devillei and the same dimensions of the 

 upper milk molars of P. peruanum are quoted from Sefve 

 and arranged in the following table. 



Dimensions of Molars of Parahipparion in millimeters. 





M 1 



M 2 



M 3 





(-1 



£ 



T3 

 f 



■43 



be 



£5 



<D 

 1-1 





"So 

 a 



IB 



fl 



■S 



^ 



Parahipparion bnrmeisteri 



P. saldiasi 



295 



29- 



25- 



27- 

 24- 



30- 

 29- 

 27- 

 25- 

 25- 



29" 

 26- 



23 : 



29-5 



26- 



88- 



27- 

 32-5 



24 : 



24- 

 22- 



P. bolivianum 





P. devillei 



P. devillei .. 



21- 





D 1 



D* 



D 3 



P. peruarmrn 



35-7 23- 



28- 22-5 



29-2 22- 



The width of the crown of the upper molar from Ayusbamba, 

 viz., 22 mm , is less than that recorded, in the table, for m 1 of any 

 species of Parahipparion. P. devillei comes nearest, with a 

 width of 25 mm for m 1 , while P. saldiasi and P. bolivianum 

 are much farther removed. A direct comparison with the first 

 molar of P. peruanum is impossible, the permanent upper molars 

 of that species being unknown ; but as far as any inference can 

 be drawn from the transverse dimensions of the deciduous teeth, 

 I should expect to find the width of m 1 of P. peruanum about 

 equal to that of P. saldiasi. Whether this inference is correct 

 or not, the isolated upper molar from Ayusbamba is evidently 

 from some small-sized species of P arahipparion. 



The posterior portion of the skull of Parahipparion has 

 never been described, although five species of the genus have 

 been recognized. The only cranial parts, besides the teeth, 

 that have previously been collected, are the maxillary, premax- 

 illary and palatine elements, and the mandible. Therefore 

 the Yale Expedition was fortunate in securing at Ayusbamba a 

 skull apparently belonging to this genus. This specimen, 

 though far from complete, is composed largely of parts regard- 

 ing which we have had no definite knowledge. A careful 



