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 hzards 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 pecuhar 

 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 Austraha, 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 Austraha and Tas- 

 mania, Echidna in Austraha, Tasmania, and New 

 Guinea, and Proechidna in New Guinea only. 



The marsupials are extraordinarily numerous and 

 very diverse, and a pecuhar feature is that the more 

 speciahzed 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 

 Mnk 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 



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