vi] DISTRIBUTION OF SELECTED GROUPS 123 



A peculiar flying form is Anomaliirus, the palm- 

 marten of West Africa. Other outlying forms are 

 the jumping hares, Pedetes, of the South African 

 veldt. 



Beavers of temperate and cool Eurasia came late 

 into North America. 



Rats and mice are absolutely cosmopolitan. Even 

 Australia has several peculiar genera : the aquatic 

 Hydromys, the Queensland rat Xeromys and several 

 'jumpers.' Many genera in Eurasia and North 

 America, whence steadily decreasing through Central 

 into South America. Remarkable are the Dipodidae, 

 known from American Eocene onwards : Zapus in 

 Canada and China ; alactagas and jerboas from 

 Eastern Asia to North Africa, the former extending 

 into interglacial Europe as typical steppe-creatures. 

 The brown rat is Asiatic, crossed the Volga in 1727, 

 arrived in Germany in 1770, shipped a few years 

 later to North America and has since overrun the 

 whole world. 



Porcupines in the wider sense, or Hystrichomorpha, 

 are important : Afro- Indian and tropical American ; 

 whilst many fossils are known from European Eocene 

 and Oligocene, none occur in North America. Chin- 

 chillas, agutis, guinea-pigs, etc. live in Central and 

 South America. Porcupines : Hystrix mid-Miocene 

 in Europe, now Afro-Indian ; prehensile-tailed tree- 

 porcupines, e.g. Synetheres, from Bolivia to Mexico ; 



