XI PALAEONTOLOGY AND EVOLUTION 3C9 



promulgated as "the law of the succession of 

 types " is, that, in all these provinces, the animals 

 found in Pliocene or later deposits are closely 

 affined to those which now inhabit the same pro- 

 vinces ; and that, conversely, the forms character- 

 istic of other provinces are absent. North and 

 South America, perhaps, present one or two 

 exceptions to the last rule, but they are readily 

 susceptible of explanation. Thus, in Australia, the 

 later Tertiary mammals are marsupials (possibly 

 with the exception of the Dog and a Rodent or two, 

 as at present). In Austro-Columbia, the later 

 Tertiary fauna exhibits numerous and varied forms 

 of Platyrrhine Apes, Rodents, Cats, Dogs, Stags, 

 Jfdentata, and Opossums ; but, as at present, no 

 Catarrhine Apes, no Lemurs, no Insectivora, Oxen, 

 Antelopes, Rhinoceroses, nor Didelphia other than 

 Opossums. And in the widespread Arctogaeal 

 province, the Pliocene and later mammals belong 

 to the same groups as those which now exist in 

 the province. The law of succession of types, 

 therefore, holds good for the present epoch as 

 compared with its predecessor. Does it equally 

 well apply to the Pliocene fauna when we com- 

 pare it with that of the Miocene epoch? By 

 great good fortune, an extensive mammalian fauna 

 of the latter epoch has now become known, in 

 four very distant portions of the Arctogaeal pro- 

 vince which do not differ greatly in latitnd*. 

 Thus Falconer and Cautley have made known the 

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