72 



PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



and those of P. cavum, the postero-internal cusp, or tetartocone, being 

 smaller than in the former species, larger than in the latter. In m- the 

 progress of abrasion has united the posterior conule with the hypocone, 

 as in P. atistrale, and in both m- and m- between the two internal cusps 

 is a minute pillar, which is present, though apparently not constant, 

 in many of the species, but attains importance only in P. acre (q. v.). 

 M- agrees closely in size with that of P. perJ>olitum and also in the very 

 unusual feature that the two external lobes of this tooth are of nearly 

 equal width. It differs, however, from the latter species in the develop- 

 ment of the hypocone, which is larger than in any other species which I 

 have observed, but is wanting in P. perpolitum. In the mandible, the 

 canine is separated by unusually short diastemata from the tusk and p^. 

 The latter is very small and has a single cylindrical root. 



In the succeeding table. No. 20 is a cast of the type-specimen ; No. 

 9267 is in the collection of the American Museum and No. 15,996 in that 

 of Princeton University. 



Measurements. 



Upper dentition, length i-2. - m-^ 

 I-^, antero-posterior diameter 



" transverse diameter 

 Upper premolar-molar series, length 



" premolar series, length . 

 pi, length {i. e., antero-posterior diameter) 



" width (i. e., greatest transverse diameter) 

 P^, length 



" width 

 P-^, length 



" width 

 PA, length 



" width 

 Upper molar series, length 

 Ml, length 



" width 

 M^, length . 



" width 

 M-?-, length 



" width 



No. 

 9267. 



.094 



.007 



.006 



.070 



.036 



.0075 



.006 



.008 



.0105 



.0105 



.012 



.011 



.0145 



•03 s 



.012 



.016 



.013 



.017 



.0115 



.0165 



No. 

 20. 



No. 

 15,99^- 



