336 ON A QUADRUPED. 



As this animal exhibits the character of flat crown- 

 ed teeth, altogether destitute of radicles, combined 

 with robust and absolutely perfect clavicles, it is by 

 the latter character at once excluded from Cuviers 

 second division of the Rodeniia, which comprehends 

 Lepus, Lagomys and Histrix, together with the se- 

 veral genera formed on the demolition of the Lin- 

 nsean genus Cayia. 



Of the two divisions, therefore, into which the Tlo- 

 dentia have been separated, from the consideration 

 of the presence or absence of perfect clavicles, the 

 new genus Isodon unquestionably belongs to the 

 first and may be grouped with Arvicola, Fiber.* and 

 Georyehus. It corresponds with the former, in the 

 entire and prismatic form of the teeth But in these 

 genera each jaw is furnished but with six teeth, which 

 is a smaller number by two than exists in our ani- 

 mal ; and as this numerical character is undoubtedly 

 essential, we are justified in regarding it as distinct 



*Illiger enumerates four molares to each series in the jaw 

 of Fib< r ; but, after ample examination, I agree with Dauben- 

 ton and Ctivier in asseiting that but three exist ; of these the 

 grinding surface of the anterior one in the lower jaw is as long 

 as the 'wo others laken together, and is divided into nine trian- 

 gular prisms, of which the anterior and posterior ones extend 

 the whole width of the to<;th, whilst the seven other prisms are 

 smaller and alternate ; in neither of the other molares of either 

 jaw does the number of prisms exceed five. Each of these mo- 

 lares is certainly divided into two parts at base, though it is 

 true these roots are not solid. 



