330 Kew Gumts of Mammalia called Uydroinis, 



outstripped by commerce, that I could not help embracing 

 the earliest opportunity of endeavouring to discover to what 

 animal this useful fur belonged. Among the number of 

 skins which M. Bechcni possessed, I had the good for- 

 tune to find a siifficient number entire, to enable me to hope 

 that I should be able to determine this point. I soon per- 

 ceived that the^dcscription of the qnonyia of M. d'Azzara 

 corresponded to them perfectly, and th.it this description 

 could be exactly applied also to the drauing of the mijopo- 

 tuvnis. 1 should have been sooner conducted to this com- 

 parison, had I not, found, in the French translation of 

 M. d'Azzara's work, the epithet of red twice substituted for 

 that of ruddy : the author, by the Spanish word mbro, had 

 denoted only the latter quality. 



It was with reason that Comnicrson had provisionally 

 considered his animal of Buenos-Avres as a new genus : it 

 belongs to the order of \h& rodentia by its two strong incisor 

 teeth in each javi' ; but not to any of the genera of that 

 order, in consequence of its tail and its hind feet. The 

 conjecture of Commerson Is now^ fully justified by the ex- 

 istence of two other species in New Holland, which have 

 exactly the same combinations of form : such are the three 

 animals which I comprehend under the same generic deno- 

 mination of hijdroviis. 



To be able to subdivide with "more precision the order of 

 the rodentia, and particularly the numerous genus of rats, 

 H'e have attended to the consideration of the molar teeth, 

 the form of which has furnished us with excellent charac- 

 ters, which have gone hand in hand with the different con- 

 figurations of the feet and the tail. Thus, all the rats ana- 

 logous to the field rat, the water rat, &c. have the molar 

 teeth formed of laminae placed one before the other, and 

 the tail short atrd hairy : on the other hand, those which 

 have a relation to the common rat, See, Norway rat, &c. 

 arc distinguished by molar teeth with a simple crown, and 

 by their long tail, which is in part naked and scaly ; others, 

 such as the hamster, have these teeth single, and the tail 

 short and hairv. 



My first care, after these observations, ought to be to at- 

 tend to the molar teeth of my three species, and deduce 

 from them characters applicable only to them. I was de- 

 prived of the moans of doing this in regard to the American 

 species. M. d'Azzara neglected to speak of its molar 

 teeth : Molina, however, has in part supplied this defi- 

 ciency, if it be true that he extended his remarks to their 

 number. We have reason to believe this from the extract 



7 in 



