338 ON A QUADRUPED. 



cation, the tooth becomes much worn, the folds of 

 enamel are insulated from the sides of the looth, and 

 represent elongate- oval figures on the disk, that gra- 

 dually diminish in size with the advancing age of the 

 animal. The corresponding teeth of Ccelogenus, 

 equally participate in this property. The attrition 

 of mastication, on the contrary, produces no visible 

 effect whatever, in modifying the configuration of the 

 folds in the teeth of the animal under consideration, 

 for these are precisely similar at the end of the tooth 

 which rests upon the bottom of the alveole, as at the 

 grinding surface : and in this respect, agreeably to 

 preceding observations, corresponding with Arvicola, 

 and, I may also add, with Pseudostoma.* 



But Ccelogenus f differs from all other LinnaeanCa- 

 vys, and agrees with Isodon in the number of its toes, 

 though this coincidence is not extended to the pro- 

 portions of these members to each other, their inner 

 toes being small and weak, and those of the poste- 

 rior feet being raised a little from the earth, aid but 

 little, if at all, in supporting the body ; whereas those 

 of the subject of this essay, all press firmly and ef- 

 fectually upon the soil in walking. 



These traits of resemblance, however, are either 



* Long's expedition to the Rocky mountains, Vol. I. 



t A cranium of C.fulvus of F. Cuvier, in the Philadelphia 

 museum, corresponds, in its remarkably eroded appearance, 

 with that of the French museum, as described by that author. 



