70 THE ANATOMY OF INVERTEBRATED ANIMALS. 



There is no doubt that provinces of distribution, closely 

 corresponding with these, existed at the time of the Qua- 

 ternary and later Tertiary rocks. In Europe, North America, 

 and Asia, the Arctogaeal province was as distinctly charac- 

 terized in the Miocene, and probably in the Eocene epoch, as 

 it is at present. What may have been the case in Austroco- 

 lumbia, Australasia, and Novozelania, we have no means of 

 being certain, in the absence of sufficient knowledge of the 

 Miocene and Eocene deposits of those regions. 



Our present knowledge of the geographical distribution 

 which obtained in the older periods does not enable us to 

 speak with any confidence as to the limits of the provinces of 

 distribution in the past. But this much is certain, that as far 

 back as the epoch of the Trias — at the dawn of the Secondary 

 period — the Meptilia and Amphibia of Europe, India, and 

 South Africa, and probably North America, presented the 

 same kind of resemblance as the mammals and birds of the 

 corresponding Arctogaeal fauna do now. But then there is 

 no information respecting the reptiles and amphibians of the 

 corresponding epoch in Austrocolumbia and Australia, so that 

 it is impossible to say whether, in Triassic times, the Arcto- 

 gaeal province was limited as it is now. 



Outside the limits of the Arctogaeal province, the mate- 

 rials for forming a judgment of the distribution of animals 

 are altogether insufficient to enable us to draw any conclu- 

 sion as to the existence, and still less as to the boundaries, of 

 definite provinces of distribution in Palaeozoic times. No 

 remains of land-animals have yet been discovered. The 

 fresh-water fauna consists of Amphibians and Fishes, and we 

 know nothing, or next to nothing, of these in any part of the 

 world except the Arctogaeal province. 



A good deal is known of the older Silurian fauna outside 

 the boundaries of the present Arctogaeal province, and within 

 those of both the Austrocolumbian and Australasian prov- 

 inces. With a generally similar fades, the faunae of these 

 regions present clear differences. And, considering that the 

 groups of animals which are represented are chiefly deep-sea 

 and pelagic forms, it is not wonderful that this similarity of 

 facies should exist. The investigations of the Challenger 

 expedition show that such forms present a like similarity of 

 facies at the present day. 



One of the most important facts which have been estab- 

 lished under the head of Zoological Chronology is, that in all 

 parts of the world the fauna of the later part of the Tertiary 



