1903] Matthew^ Fauna of Titanotherium Beds of Montana. 2 1 3 



have both originated from the valleys and lateral notches of 

 a brachyodont molar, such as that of Ischyroniys. Either of 

 these is easily derivable from a primitive tritubercular molar 

 such as those of the Tillodonta, but not easily from such teeth 

 as are displayed by Par amy s and its allies, in which, as in 

 the squirrels, the teeth appear to be specialized and degen- 

 erate rather than primitive. 



The upper jaiv of Cylindrodon (No. 9639) is that of an old 

 individual, with but little indication of the pattern left on 

 the teeth. From what there is present it appears that the 

 pattern exhibited a strong median external inflection and an- 

 terior and posterior fossettes, and a trace remains on p* of an 

 internal inflection. The pattern was probably like that of 

 Ischyromys, in having the external inflection of greater per- 

 sistence and depth than the internal. In other Castoridse this 

 condition is reversed. The upper molars decrease in size from 

 before backward and are of rounded peg-like outline, fossettes 

 on all but m^ The incisor originates just above the roots of 

 p4 and m\ and is stout, not grooved, with a moderate dias- 

 tema between it and the grinding teeth. The antorbital fora- 

 men is small and the palate in front of it is narrow. 



The depth of the jaw of Cylindrodon in its anterior portion 

 is a very marked character. Ischyromys comes nearest to it 

 in this respect. 



SCIURID.'E. 



Sciurus (Prosciurus) vetustus, subg. et spec, no v. 



Represented by an upper jaw, No. 9626, with complete un- 

 worn dentition. 



The species is smaller 

 than 5. relictus of the 

 Oreodon Beds, and at 

 least a third smaller than 

 S. jefjersoui Douglas of 

 the Pipestone Creek 

 Beds, or 5. ■wortmani of 



the John Day formation. Fig. q. Sciurus vetustus. Crown view of upper 



•^ -^ teeth, four times natural size. Type. 



It is larger than 5. hailo- 



vianus of the John Day, the first molar (the only upper tooth 



