182 Annals of the Carnegie Museum. 



many times larger but not nearly so large as Mi. The teeth are 

 intermediate between those of Scinrus and Arctoniys, rather more 

 resembling some species of the former. On Pi and Mi the three 

 cross-crests are very distinct and the posterior cingulum is well 

 developed. From the Loup Fork beds, Lower Madison Valley. 



Fig. Sciunis arctoviyoiJcs [y^o. 741;. Lower Madison Valley. Natural size. 



The lower incisor is laterally compressed and has minute striations 

 on the anterior face, like the upper ones. P^ is smaller than any of 

 the molars and has four tubercles. My and M^- have four tubercles 

 each and minute inner and outer intermediate ones. The teeth are 

 oblique, as in Arctoiiiys /noiiax, only not so much so. All the molars 

 are nearly of the same size. The* mental foramen is placed quite far 

 forward, being considerably in advance of the premolar. The anterior 

 angle of the masseteric area is higher than in Arctomys and extends 

 far forward, being a little below the premolar. 



Measurements. 



Mm. 



Length of the anterior upper cheek teeth 8 



" of last premolar 3 



Width of last premolar I-I 



Length of lower molar-premolar series 16 



" from incisor to pi 12 



Depth of mandible under My 12 



Pal^arctomys gen. nov. 

 No. 740. Fig. 23. 

 Teeth nearly like those of Arctomys, but small in proportion to the 

 size of the skull. Incisors large and strong, with many minute inter- 

 rupted longitudinal striations and two or more larger convex ridges 

 separated by shallow longitudinal furrows on the anterior faces. 

 Skull large and strong anteriorly, in this respect differing much from 

 Sciurus and Arctomys. Temporal ridges uniting farther forward at a 



