440 MILLER AND GIDLEY: SUPERGENERIC GROUPS OF RODENTS 



Paramys, My sops, Prosciurus, and related genera; North American 

 Lower Eocene to Middle Oligocene. 



B. — Skull and teeth as in the Paramyids except that the auditory bullae 

 are well developed, the infraorbital foramen is enlarged to transmit a small 

 strand of muscle, and the cheekteeth are flattened. 



Family Graphiuridae 



Cheekteeth |, brachydont, crowns wider than long, basin-shaped 

 with small tubercles and low ridges (parallel: M uscardinidae) ; skull 

 with no special peculiarities, the braincase much wider than rostrum; 

 auditory bullae globular; external form muscardinine. 



Graphiurus; Recent; Africa. 



C. — Skull fossorial (except perhaps in the Allomyidae); infraorbital 

 foramen not transmitting muscle; auditory bullae well-developed; cheek- 

 teeth brachydont, hypsodont, or ever-growing; modification of crownsbased on 

 a structure including well developed protoconule and metaconule, and con- 

 spicuously trenchant outer commissures. 



Family Allomyidae 



Cheekteeth f , brachydont or moderately hypsodont, the trituber- 

 cular structure of upper teeth evident in unworn crowns; protoconule 

 and metaconule large; functional cusps in m^ and m'-; mesostyle appear- 

 ing in hypsodont forms as a conspicuous median rib on outer surface of 

 crown (parallel: Pseudosciuridae). 



Allomys, Haplomys,^ Meniscomys, Mylagaulodon; North American 

 Upper Oligocene and Miocene. 



Family Aplodontiidae 



Like the Allomyidae but the skull greatly widened posteriorly, the 

 auditory bullae flask-shaped with neck directed horizontally outward; 

 cheekteeth growing from persistent pulp, the unworn caps showing 

 evident pattern of the Allomys-i:y]iQ, this soon wearing away and leaving 

 a simple enamel ring; paramere with conspicuous vertical ridge. 



Aplodontia; Pleistocene and Recent; Liodontia,^ Miocene; western 

 North America. 



Family Cylindrodontidae 



Skull fossorial with braincase slightly wider than rostrum; cheek- 

 teeth ^, subterete, excessively hypsodont but not growing from persist- 

 ent pulp, the enamel pattern in considerably worn upper teeth consist- 

 ing of an outer ring and a central lake. 



■ Cylindrodon; North American Lower Oligocene. Position of group 

 doubtful. 



New genus, type Meniscomys liolophus Cope. 

 New genus, type Aplodontia alexandrae Furlong. 



