PAL^OMASTODON. 



14c 



the outer one is the more rounded and always much more worn than the inner, which 

 is higher and somewhat compressed from before backwards. The outer cusps, 

 particularly the anterior ones, often give a roughly V-shaped surface in wear, the 

 point of the V being turned outwards : this results from the presence of small and 

 slightly developed accessory tubercles connected with the inner side of the main 

 outer cusps. In the case of the anterior cusp the front accessory tubercle is fused 

 with the cingulum, while the posterior one partly fills the valley between the first 

 and second ridges. In the last molar the posterior accessory tubercle of the last 

 outer main cusp is larger and is connected with the cingulum, forming a small and 

 slightly developed talon. In some other species this is much larger, and the 



Text-fig. 50. 



m2. 



mx 



D. 



m 2. 



TTl 3. 



^"^^^ -^^\ J^--- 



m.i. 



The second and third lower molars of : A, Palceomastodon ieadnelli (left side) ; B, P. wintoni 

 (left side) ; C, P. parvus (right side) ; D, P. minor (right side). All § nat. size. 



accessory tubercles are better developed. The cingulum is only slightly developed : in 

 some cases it forms small blunt tubercles opposite the inner ends of the transverse 

 valleys (see PI. XV. fig. 1, m. 2). 



Vertebral Column. — The vertebral column in the present genus is not well known, 

 because the absence of specimens occurring definitely associated with portions of the 

 skull and mandible, together with the intermingling of vertebrae of other Ungulates of 

 similar size, makes it almost impossible to determine isolated vertebrae. In the case, 

 however, of highly characteristic vertebrae like the atlas and axis, some degree of 

 certainty may be attained. These two vertebrae are here described from specimens 



