150 Eaton — Vertebrate Fossils from Ayusbamba, Peru. 



cheek teeth (p 2 and p 3 ) are accordingly represented together in 

 text-figure 5. Owing to their imperfection exact measure- 

 ments cannot be taken ; but the length and width of their 

 crowns appear to have been approximately as follows : p.,, 

 length 29 ram , width 14-2 mra ; p 3 , length 2T mm , Width 16 mm . These 

 dimensions and the pattern of the enamel foldings show that 

 the teeth cannot be referred either to Equus ourvidens or to 

 any of the three species of Hippidium whose teeth have been 

 minutely described and figured by Sefve.* Their affinity lies 

 rather with the genus P arahipparion. In view of the diffi- 

 culties that beset the study of isolated equine teeth, especially 

 those of the lower series, it would perhaps be unwise to attempt 

 the specific identification of these two lower premolars ; but it 

 is significant that among all the teeth with which they have 

 been compared, they most nearly find their counterparts in 

 the first and second lower deciduous molars, and the first 

 molar, of Parahipparion peruanum from Tirapata, Peru, fig- 

 ured by Sefye.f The united length of the first two milk 

 molars of this last mentioned specimen amounts to approxi- 

 mately 56 mm ; and this measurement exceeds the restored 

 united length^ of the two teeth under discussion by 2 mm , which 

 is very nearly the difference in length that one might expect 

 to find between the first and second lower deciduous teeth and 

 their permanent successors. So many variable and uncertain 

 factors enter into these measurements that the comparison 

 should not be carried too far. 



In another lower cheek-tooth (p„) from Ayusbamba the forms 

 of the inner valleys (text-figure 6) are simpler than in the 

 teeth last described, the contrast in this respect being almost 

 too marked to be readily accounted for by the fact that the 

 teeth present different stages of wear. It should be noted that 

 the teeth shown in text-figures 5 and 6 possess, in common, a 

 very deep outer valley that penetrates between the inner val- 

 leys and nearly traverses the crown. The deepening of the 

 outer valley, according to Sefve's observation, characterizes 

 P. devillei and P. peruanum, and distinguishes them from 

 P. saldiasi. The premolar of text-figure 6 measures, on the 

 crown, 29 mm x 14 mm . In its enamel pattern, as well as in its 

 size, it is remarkably like the p 2 of P. devillei^. which has a 

 length of 28 mm and a width of 13 ram . Although the species of 

 the Ayusbamba specimen is not determined by the above com- 



*Die Fossilen Pferde SiidAmerikas ; Kungl. Svenska Vet. Hand., 1912, 

 Band 48, No. 6. 



f Hyperkippidiuru ; Kungl. Svenska Vet. Hand., 1910, Band 46, No. 2, 

 Taf. 2, Fig. 4. 



t The nnited length of overlapping teeth is less than the sum of their indi- 

 vidual lengths. 



tSefve, 1912; Taf. 2, Fig. 21. 



