POLYMASTODONTID^. 



199 



The following specimens are not specificall)j determined. 

 48399. Fragment of the left ramus of the mandible, showing the 

 three premolars, and a detached fourth lower premolar ; 

 from the Middle Purbeck of Durdlestone Bay. 



BecMes Collection. Purchased, 1876. 



Family POLYMASTODONTIDiE. 



In the one known genus of this family the dentition is I. j, 

 C.^, Pm.p M. -. The premolar is tubercular, and agrees in 

 structure with the true molars, although somewhat simpler; the 

 true molars are elongated antero-posteriorlj, those of the ui)per jaw 

 having three ridges, m. 1 being longer than iK72 and having six 

 tubercles on each side. The angle of the mandible is inflected ; the 

 humerus has no entepicondylar foramen, and the astragalus is 

 without a trochlea ; the caudal vertebrae indicate a large tail. 



Fig. 32. 



Polymastodon taoensis. — a, h, c, d. Right mandibular ramus ; from tlie Puerco Eocene of New 

 Mexico. <?. Fragment of a maxilla. |. (From the ' Amer. Nat.') 



