MILLER AND GIDLEY: SUPERGENERIC GROUPS OF RODENTS 439 



ing from the symmetrical plan; crowns brachydont or slightly hyp- 

 sodont; manus normal. 



Tlie Murinae of authors; Upper Miocene to Recent; Old World, 

 except Madagascar. 



Subfamily Phloeomyinae. — Upper cheekteeth with triserial arrange- 

 ment of elements obscured by flattening out of each trio of tubercles to 

 form a simple, detached, transverse lamina (parallel: Diplomys); 

 crowns moderately hypsodont ; braincase relatively small and auditory 

 bullae reduced; external form heavy, arboreal. 



Phloeomys; Recent; Philippine Islands. 



Subfamily Otomyinae. — Upper cheekteeth with same modification as 

 in the Phloeomyinae, but m^ tending to become the dominant tooth in the 

 series, its size always greater than that of m^, and its elements usually 

 reduplicated; external form heavy, terrestrial. 



Otomys; Recent; Africa. 



Subfamily Hydromyinae. — Upper cheekteeth with triserial arrange- 

 ment obscured by suppres^on of tubercles of outer series; m'' vestigial. 

 The Hydromyinae oi anthoYs; Recent; Australian Region. 



Superfamily DIPODOIDAE 



Masseter lateralis superficialis with anterior head not distinct, this 

 portion of the muscle attaching along a considerable area on anterior 

 border of zygoma; zygomatic plate nearly horizontal, always narrow 

 and completely beneath infraorbital foramen. Angular portion of 

 mandible not distorted outward at base to permit free passage of a 

 branch of the masseter lateralis, its general direction not parallel with 

 zygoma. 



THREE-CXJSPED SERIES 



Modifications of teeth based on an underlying tritubercular structure, 

 the hypocone when present not entering into the essential mechanical 

 scheme of the crown. 



A. — Skull with no special pecularities except that the auditory bullae 

 appear to he imperfect or absent (perhaps merely reduced as in Phloeomys) ; 

 infraorbital foramen not transmitting muscle; cheekteeth brachydont or 

 subhyposodont, their structure essentially as in the less modified Sciuridae. 



Family Paramyidae 



Rostrum and braincase approximately equal in width, infraorbital 

 foramen very small, not visible in lateral view of the skull; cheekteeth 

 f , the upper molars obviously and simply tritubercular in general plan, 

 the hypocone, when present, appearing as a supplement to the original 

 structure of the tooth. 



