EDENTATA OF THE SANTA CRUZ BEDS. 33! 



PREPOTHERIUM MOYANI Ameghino. 



(Plate LX, Figs, i, i.) 



Prepotherium moyani Amegh. ; num. Synopt. des Mamm. Foss. de Pata- 

 gonie, 1894, p. 162. 



This species, which is as yet known only from the type, is of nearly the 

 same size as the preceding one, but differs in the form of the teeth and 

 the character of the mandible. The molariform teeth have a more oval 

 grinding surface than in P. filholi, with the transverse crests more curved 

 and less parallel, while the antero-posterior compression is much less ex- 

 treme ; another distinction is that - is larger than -, while in the preceding 

 species - and - are of almost equal size ; - has a deep vertical groove on 

 the posterior side, producing a reniform grinding surface, as in both of 

 the species of Planops. 



Unfortunately, the mandible is far from complete, but the portion pre- 

 served is highly characteristic ; the peculiarity consists in the very great 

 vertical depth of the horizontal ramus in the dentary region, with ex- 

 tremely convex ventral border, which rises steeply behind and becomes 

 concave below the ascending ramus ; anteriorly, the rise is very gradual, 

 much more so than in P. filholi, and indicates a very long predental 

 beak. The animal appears to have been fully adult and yet the jaw has 

 on its outer side a large number of minute vascular foramina, producing 

 a surface texture unlike that of any other contemporary species. The ex- 

 ternal dental foramen has a slightly lower position than in P. filholi and 

 is considerably larger, especially in width. 



The resemblance of this mandible to that of Megatherium is very strik- 

 ing and suggests that the ancestor of the latter was allied to the present 



species. 



MEASUREMENTS. 



Upper dentition, length 060 T , length 007 



" " " 1-A 042 " width 006 



1, length (i. e., antero-posterior diam- ^, length 0095 



eter) 009 " width 0135 



" width (i. e., transverse diameter) . . . .007 ^, length 009 



, length 0085 " width 0145 



" width 0115 f, length 0105 



3-, length 0095 " width 014 



" width 014 Mandible, depth below -g 046 



Lower dentition, length 050 " " " 040 



" M 036 



