72 Annals of the Carnegie Museum. 



mm. 



Antero-posterior diameter of M T 21 



Transverse diameter of M T 10 



Antero-posterior diameter of M j 7 



Transverse diameter of M^ 5 



RODENTIA. 



Fig. 20, which is here given, represents what appears to be an upper 

 premolar tooth which was found in the Upper Harrison 

 beds, two miles north of Agate Spring Fossil Quarry in 

 Sioux County, Nebraska. The tooth may represent an 

 Fig. 20. undescribed genus related to Menis corny s or a primitive 

 Tooth of mylogaulid. In outline the tooth is less triangular than 

 o en . T . t j ie f ormerj an( j f ] ess antero-posterior diameter than that 

 in Mylogalus. The tooth is deeply grooved on the sides, plainly indi- 

 cating the position of the two roots, which are fused together. 



