564 



SB. F. AMEGHINO ON THE 



[May 2, 



seuts the unworn fifth riglit lower inohir of yirc/freop/nZMspairiMS, 

 from the Upper Cretaceous ; the six cusps are perfectly distin- 

 guishable, although very low and disposed a little differently. 

 The cusp inp, which is very large and completely separated from 

 cusp pe, has moved to the internal side, and these cusps disappear 

 without leaving any trace as soon as the teeth begin to be 

 functional; so that the molar acquires an entirely different contour 

 and appearance, as shown by fig. \\h, representing the same tooth 

 of an adult specimen. 



In the unworn lower molars of Prosotherium, another Cretaceous 

 genus of the same order, the cusps ma and nip are placed 

 towards the outer side, so that the six cusps are disposed in two 

 longitudinal series separated by a deep longitudinal furrow. The 

 cusps ae and ai being also higher and thicker than the others, the 

 ci'own assumes a certain resemblance to that of the molar of 

 Microlestes antiquus, a very remarkable and suggestive fact. 



The origin of the molars of Primates is the same. Here, too, 

 as in the bunodont Ungulata, the mound-shaped, bulky, and thick 

 cusps, characteristic of the omnivorous condition, are a recent anil 

 gradual acquisition. 



Fig. 12. 



coe. 



Notopitheaus fosstdatus : fifth right lower molai-, slightly woi-n, external (a) 

 and superior {h) respect, tour times nat. size. — Upper Cretaceous ; Patagonia. 



-m^ ^ 



Pitheculus australis : fifth right lower molar, superior {a) and external (4) 

 aspect, four times nat. size. — Upper Eocene; Patagonia. 



Fig. 12, a, h, exhibits the fifth lower molar, not much worn, 

 of Notopithecus fossulatus. from the Upper Cretaceous, external 

 view and upper view. This tooth shows distinctly, although not 



