448 MILLER AND gidley: supergeneric groups of rodents 



MEDIALIS SERIES 



Masseter medialis the chief agent in modifying form of outer side of 

 mandible; a conspicuous horizontal ridge for the attachment of this 

 muscle present on side of mandible slightly below alveolar level. 



Family Caviidae 



Posterior cheektooth both above and below without reduplication of 

 elements, the general character of the toothrow normal. 



The Caviidae of authors with Hydrochoenis and its allies removed; 

 South America; Miocene to Recent. Extinct genera: Anchimys, Neo- 

 procavia, Orthomyctera, Palaeocavia, Phugatherium, Procardiotherium. 



Family Hydrochoeridae 



Posterior cheektooth both above and below with conspicuous redupli- 

 cation of elements, the general character of the toothrow thus rendered 

 abnormal. 



Hydrochoerus and its extinct allies Plexochoerus, Prohydrochoerus 

 and Protohydrochoerus; perhaps Cardiomys, Caviodon ( = Diocariherium) 

 and Cardiotherium also; South America, Miocene to Recent; south- 

 eastern United States, Pleistocene. 



