174 



" The ArvicolidfE appear to be confined to North America and the 

 European province. In South America they are apparently replaced 

 by the Octodontidce, ChinchillidcB, and Caviida. 



" The family LeporidcB is but feebly represented in each of the 

 provinces above-mentioned, excepting in North America, where the 

 number of species already discovered is almost equal to all those 

 found in other portions of the globe taken together. In earlier pe- 

 riods, these Rodents, which are very low in the scale, appear to have 

 been much more numerous, judging from the fossil remains which 

 have been found, — at least in the European province. 



" The remaining families of Rodents are almost entirely confined 

 to South America. The genus Aulacodus of Western Africa, the 

 genera Petromys, an inhabitant of the Cape of Good Hope, and 

 Bathyergus, found both at the Cape and north-east portions of 

 Africa, possess certain characters in which they approach the South 

 American forms. Petromys analogically appears to represent the 

 Octodons of South America, and Bathyergus may be compared to 

 the genera Poephagomys and Ctenomys; whilst in Aulacodus we 

 possess a representative of the Capromys of the West Indies." 



Mr. Waterhouse observed " that he had not yet been able to satisfy 

 himself as to the precise situation, in a systematic classification, of 

 the genera Ctenodactylus and Helamys, the former from North, and 

 the latter from South Africa. Four other genera are omitted in the 

 above table for the same reeison ; they are, Otomys* of Dr. Smith, a 

 genus found at the Cape of Good Hope ; Akodon, Meyen, which in- 

 habits Peru ; Heteromys, Desmarest, founded on the Mus anomalus 

 of Thompson, an animal found in the island of Trinidad ; and lastly, 

 Saccomys of F. Cuvier, which is supposed to be from North Ame- 

 rica. These four genera in all probability belong to the family 

 Muridce. 



" The genus Aplodontia is placed with the Sciuridce, but it must 

 be observed that it differs much from the typical species of that 

 group, there being no post-orbital process to the skull, and the molar 

 teeth being rootless. 



" The remains of Rodents found in a fossil state indicate that the 

 different provinces were formerly inhabited by the same forms as 

 those which are now found in them." 



* This is a different genus to the Otomys of Cuvier, which is Euryotit of 

 Brants. 



