SUBORDER A 



SIMPLICIDENTATA 



105 



Subfamily 1. Aplodontiinae Thomas. 



Cheek teeth, as a ride, hrachjodont. In place of the cusps they have irregular, 

 non-parallel ridges. 



Sciurodon Schlosser. Phosphorites of Quercy. 



Meniscomys Cope {Allomys Marsh). Lower Miocene. John Day beds ; 

 Oregon. 



Mylagaulodon Sinclair, Lower Miocene ; Montana. 



Haplodon Rafin. Hypsodont. Recent, Pliocene and Pleistocene of North 

 America. 



Subfamily 2. Ischyromyinae Alston. 



Cheek teeth brachyodont. Eocene and Oligocene of North America. 



Ischyromys Leidy (Fig. 129). Both pairs of cusps of the upper M are 

 opposite, of the lower Tlf they are alternating. Oligocene. White River beds. 

 Mysops Leidy (Tillomys Marsh). Eocene. Bridger beds. 



Fig. 129. 



Ischyromys typus Leidy. Oligocene 

 of White River beds. A, Upper and 

 B, lower tooth-row. 3/i. 



Fig. 130. 

 Faramys delicatus Leidy. Middle Eocene. Bridger 

 beds of Wyoming. Skull and lower jaw. 1/2- (After 

 Matthew.) 



Titanotheriomys Matthew. Lower Oligocene. Titanotherium beds. 



Paramys Leidy (Pseudotomus Cope) (Fig. 130). Upper M tritubercular, 

 the second pair of cusps of the lower M form the posterior border of the 

 tooth, as is practically the case also in Sciurus. Many different species in 

 the Eocene of North America. Also Lower Eocene of France. 



Plesiarctomys Bravard. Eocene. Debruge. 



Sciuravus Marsh. Upper M with four tubercles. Eocene of North 

 America. 



Family 2. Sciuroidea. 



-f- P. % M. Skull arched. Infraorbital canal small. The anterior branch 

 of the masseter is attached on the front side of the zygomatic arch. Postorhital 

 process present. Tibia and fibida not fused. 



Subfamily. Sciurinae. 



Cheek teeth are brachyodont, hmodont or lophodont. The second pair of cusps of 

 the lower cheek teeth form the posterior surface. Upper M and P "* tritubercular. 



The Sciurinae may be derived from Paramys, and have a world-wide 

 distribution. 



