ON A QUADRUPED. 337 



from either. In numerical dentition, however, Iso- 

 don agrees with Castor, Bathyergus and Helamys ; 

 but without resorting to a detail of other discrepan- 

 cies, the manner in which the folds of enamel are ar- 

 ranged in its teeth, very sufficiently distinguishes it 

 from either. 



Having thus stated the characters by which Isodon 

 is distinguishable as a genus from the various genera 

 of the Rodentia, amongst which it claims a situation 

 from the circumstance of its possessing clavicles, I 

 shall, for a moment, dispense with the consideration 

 of these important appendages, for the purpose of 

 comparing it with that section of the order, in which 

 the clavicles are rudimental both in their form and 

 functions. 



In this section, after passing over Hystrix, Lepus 

 and Lagomys, as claiming only a remote and ordinate 

 alliance, we shall discover some points of resem- 

 blance in oue of the several genera into which the Lin- 

 nsean Cavys have been judiciously distributed. 



Of these Hydrochoerus, Anoema, and Chloromys 

 of Erxleben and F. Cuvier, are in common distin- 

 guished by the number of toes, of which there are 

 four on the anterior foot and but three on the hind 

 foot; in the first and second of these genera the mo- 

 lar teeth are very remarkable and peculiar. In Chlo- 

 romys the folds of enamel in the molares seem chief- 

 ly confined to the superior portion of the tooth, and 

 proceed inward and downward into its substance, so 

 that when, in consequence of the attrition of masti- 



42 



