274 THE GEOGRAPHY OF MAMMALS 



Dinomyidse, and Caviidte, containing what are usually 

 called the Chinchillas, Agoutis, Giant-mice, and Cavies, are 

 entirely restricted within its limits, while a fifth family, 

 the ErethizontidcV, or Tree-Porcupines, has a single genus 

 in the Nearctic Region. 



The Octodontidze, a large group of seventy or eighty 

 species, divided into some twenty-two genera, are also 

 mostly Neotropical, but four peculiar types, Ctenodactylus, 

 Massoutiera, Pectinator, and Petromys forming a little 

 group by themselves, are Ethiopian. The true Porcu- 

 pines, Hystricidse, of which three genera are known, are 

 found in the Ethiopian, Oriental, and Palsearctic Regions, 

 typical Hystrix being the only one met with in Europe and 

 Northern Asia. 



Finally, at the close of the long series of Rodents, 

 we have the two groups of Pikas and Hares, markedly 

 differing from the nineteen previous families in their 

 dentition, and therefore assigned to a separate Sub-order 

 of Rodents as Duplicidentati. The Pikas (Ochotoma), of 

 which some sixteen species are recognized, are restricted 

 to the highlands of the Nearctic and Pakearctic Regions. 

 The Hares (Leporidie) have a much wider distribution, 

 having representatives in every part of the world's sur- 

 face except in the Australian Region and Madagascar. 

 Of Lepus proper some sixty species are now recognized, 

 the greater number of which occur in the Palsearctic 

 and Nearctic Regions, whilst they are generally scarcer 

 further south, though well represented in Africa. 



