ZOOGEOGRAPHICAL REGIONS 223 
The so-called American ostrich (genus Rhea), is charac- 
teristic, and is represented by several species. Among 
the negative characters we may note the absence of 
crows and ravens, which do not extend south of Guate- 
mala. As in Australia there are many parrots. Among 
the reptiles interesting forms are the rattlesnakes, the 
boas and anacondas, and the lizards of the family 
Iguanidae, while there is a large number of toads and. 
frogs, especially tree-frogs (Hylidae). Among the fish 
the dipnoan called Lepidosiren is important. 
Finally we must consider the markedly peculiar 
AUSTRALIAN region. Here the higher or placental 
mammals are absent, with the exception of bats, a few 
rodents of the mouse section, the dingo or native dog 
of Australia, and the pig of New Guinea, which is 
probably an introduced animal. As already explained, 
the region further includes the only living monotremes, 
Ornithorhynchus being found in Australia and Tas- 
mania, Echidna in Australia, Tasmania, and New 
Guinea, and Proechidna in New Guinea only. 
The marsupials are extraordinarily numerous and. 
very diverse, and a peculiar feature is that the more 
specialized forms, e.g. the certainly modern tree- 
kangaroos, occur towards the north, in Queensland and 
New Guinea, &c., whereas the more primitive forms, 
e.g. the Tasmanian wolf and Tasmanian devil, occur 
to the south, in the island of Tasmania. This is another 
link in the chain of evidence which suggests that 
Australia received its original marsupials from the 
south, through a connexion with South America, 
rather than from the north, through the islands of 
the Austro-Malayan region. We need not consider 
further the marsupials of the region beyond noticing 
that there are forms adapted to almost every kind of 
