THE NEOTROPICAL REGION 61 



Malay Peninsula. The explanation of this curious case of 

 discontinuous distribution is afforded by the past history 

 of the group. During Miocene and Pliocene times, 

 members of this genus and its allied forms were found 

 both in North America and also throughout the Old 

 World from France to China. This gives us direct 

 evidence of the former much wider extension of the 

 family of Tapirs, and bridges over the present great gap 

 in its distribution. 



As already stated, the fauna of the Neotropical Region 

 is almost as remarkable for the absence of certain families 

 as it is for the presence of peculiar forms. This is specially 

 noticeable in the Ungulates. There is no existing re- 

 presentative of the four great families of the Oxen, 

 Rhinoceroses, Horses, and Elephants in this region, though 

 remains of the latter two groups have been found in most 

 recent deposits of Argentina. Here they were probably 

 immigrants from the north, which survived but a short 

 time in this locality. 



Turning now to the Rodents, we find that out of the 

 four chief divisions into which this order is separated — the 

 Squirrels {Sciwromorpha), the Mice (Myomorpha), the 

 Porcupines (Hystricomorpha), and the Hares (Duplici- 

 dentata) — the first two and the last contain very few 

 peculiar genera and no peculiar families in this Region. 

 But, on the other hand, out of the six families of Hystrico- 

 morpha four are restricted to this region, while of the 

 remaining two, one (the Qctodontidse) is found elsewhere 

 only in Africa, and the other, the Porcupines (Hystricidw) 

 is of wide distribution. Moreover, all the Neotropical 

 genera of the Hystricomorphine division are, without 

 exception, confined to this region. 



