592 



PEOF. F. vvOOD JONES ON THE 



Lower Molars, 



The lower molar series consists of two dental masses with the 

 same simple type of occlusal surface as that displayed by the 

 upper teeth. The anterior molar is divided into two main parts, 

 and in some specimens, but not in all, a very small posterior shelf 

 is present. The posterior molar is also divided into two main 

 masses, but the whole area of the tooth is considerably less than 

 that of the anterior one. (See text-fig. 5, A.) Again there is 

 the same complexity of the alveolar cavities and roots. Again 

 9 root-cavities belong to the anterior molar mass. The anterior 

 portion of the anterior molar has a large anterior root and two 



Text-fisfure 5. 



A 



Left lower molar series of IHydromys chrysogaster. A. Occlasal surface. 

 B. Alveolar cavities, the outlines of the anterior molar being shown. 



small postero-lingual and two small postero-labial roots. The 

 posterior portion has two small labial, one small lingual, and a 

 large, transverse, and partially sub-divided posterior i"oot. There 

 are again two rather tortuous root- cavities, situated antero- 

 posteriorly, for the posterior molar. (See text-fig. 5, B.) 



Looking at the whole of the peculiar features of this upper and 

 lower molar series, with its strange collection of roots and alveoli, 

 it is difiicult to avoid conjecturing that, despite the simple crown- 

 pattern of the anterior molar it is in reality very far from being 

 a simple tooth. It is difiicult to avoid speculating as to whether 

 Hydromys has in reality simplified its dentition by the loss of a 



