188 



Annals of the Carnegie Museum. 



to the posterior portion of the incisor. It is undoubtedly much like 

 the corresponding tooth of No. 723. 



It is possible that in old age one or both of these molars were 

 shed, leaving only the prismatic premolar, as seen in M. uionodon, or 

 this tooth and M^- as in M. paniensis ? 



This species differs from M. monodon in the size of the permanent 

 premolar, in the number of enamel inflections, in the angle of the 

 mandible, and in the condyle. The posterior angle is not just like 

 anything I know in any rodent. It projects outward andjs twisted 



Fig. 26. Mylagaiilus? pristiiius (No. 742). Lower Madison Valley. Left 

 ramus of mandible. | nat. size, a, side view ; b, the same, top view showing 

 crowns of teeth ; c, the same showing section of P^ at place indicated in a, where 

 the tooth was sawed in two. 



on itself so that anterior surface faces upward and forward more than 

 outward. This terminates in a lenticular-shaped surface facing down- 

 ward, backward and, outward. 



Measurements. 



Mm. 



Length of mandible from anterior of incisor to posterior of condyle 45 

 Length of back series of teeth 13.5 



