III.] RODENTS. 91 



by the comb-like bristles on the hind feet, and their bell-like cry ; 

 two Chilian species, constituting the genus Spalacopus, being 

 distinguished by their rudimental ears. Schizodon, on the other 

 hand, of which there is a single species from the Southern Andes, 

 has the ears larger than in the tuco-tucos. The South African 

 Petromys has been regarded as very closely allied to Spalacopus^ 

 but it is more probable it should be classed with the other two 

 African genera Ctenodactylus and Pectinator, to constitute a 

 separate sub-family. The third sub-family includes all the other 

 genera, one of which (Triaulacodus 1 }, as represented by the cane- 

 rats, is Ethiopian, while the whole of the remainder are Neogaeic. 

 Many of the species are of large size, some being arboreal and 

 others aquatic. Of the latter the best known and largest is the 

 coypu (Myopotamus), widely spread over South America ; while 

 in the West Indies the group is represented by the equally large 

 arboreal hutias (Capromys and Plagiodori). The other seven 

 genera are South American, and include smaller rat-like forms, 

 which in the case of the two genera Loncheres and Echinomys have 

 flattened spines mingled with the fur; the others being known 

 as Mesomys, Dactylomys, Cannabateomys, Cercomys, and Cartero- 

 don. Several of the existing genera occur fossil in the caves of 

 Brazil and the Pampean ; Myopotamus also occurring in the 

 infra-pampean beds of Parana, together with the reputedly 

 extinct forms described as Orthomys and Morenia. Other extinct 

 genera, such as Neoremys, Scleromys, and Addphomys occur in the 

 Santa Cruz deposits, and appear to be very closely allied to 

 Myopotamus. It is noteworthy that an extinct Octodont (Pelle- 

 grinia) allied to Ctenodactylus occurs in the Plistocene or Pliocene 

 of Sicily; while Ruscinomys from the Pliocene of France is 

 believed to belong to the same group. Finally, the genus 

 Eocardia, together with certain other allied forms from the Santa 

 Cruz beds, are regarded as indicating a separate family (Eocar- 

 ditdce) of the section. 



With regard to the extinct family Theridomyida from the 

 middle and upper Oligocene of Europe, which includes not only 

 Theridomys and Archceomys, but probably also the above-men- 



1 The name Aulacodus being preoccupied, that of Triaulacodus is proposed 

 in substitution. 



