Douglass: A'ertebrates from Montana Tertiarv. 191 

 Measurements. 



Mm. 



I'"r()in fiMiit of incisor to JDack of ,, 26 



Length of alveolus of permanent premolar 6 



I -ength of dp J- 1.2 



Width " " 3 



From the Lower Madison Valley. 



Mylagaulus Paniensis ? 

 No. 731. Fig. 29. 

 A separate permanent premolar (No. 731) found in the lower Madi- 

 son Valley beds, may belong to the above named species. It is figured 

 to show the partial covering of cement which is quite thick on the 

 middle portion of the tooth, but thins out to 

 wards the top, so that the enamel is nearly bare. 



Rodent. 

 No. 802. 

 An incisor tooth from the Loup Fork beds of ;-, .^*„ 



the Lower Madison valley indicates a large rodent 

 — larger than the existing beavers. Judging by feiiKi.''fii 



its curvature it is an inferior incisor. On the 

 anterior surface there are about a dozen small , ^' ' ■ •' , 



laganiHS pameiisis l 



longitudinal striae with still smaller cross-stria- /^^q 7^1). Lower 

 tions. The striated enamel surface reaches from Madison valley. \\ 

 the anterior inner angle of the tooth, where it natural size, a, per- 

 is bounded by a longitudinal groove, to near the m^nent premolar, side 



.,,,-, r 1 • 1 view ; b, same, crown 



middle of the outer surface, where it ends 



view. 



abruptly, this surface being somewhat elevated 

 above the surface just posterior to it. The antero-posterior is much 

 greater than the transverse diameter, making it less near an ef^uilat- 

 eral triangle in section than the corresponding tooth of the Beaver, 

 Castor canadensis. 



Mm. 



Antero-posterior diameter of tooth 12 



Transverse diameter 8.5 



I .ength of portion of tooth preserved So 



