76 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



impassable by mammals since a very distant geological period. 

 Secondly, as Huxley has also pointed out, the difference be-, 

 tween South America and Arctogcea exceeds the difference be- 

 tween different parts of the latter. Thirdly, the northern part of 

 JSTorth America contains so large a proportion, not merely of families 

 and genera, but of species common to the Palsearctic region, that the 

 mammalian fauna differs less from that of Northern Asia than the 

 mammals of Central Asia do from those of Europe. Fourthl}', the 

 mammals of Madagascar differ more from those of Africa than 

 those of the Paloearctic do from those of the Oriental region *. 



* There are about a dozen mammalian genera found in Canada and the 

 northern part of the Nearctic region that are wanting in northern Asia ; of 

 these, however, several of the most important, as the Skunk {Mephitis), 

 Eaccoon (JProcyon), and Brush-tailed Porcupine {Erethizon), are Neotropical 

 forms that have found their way north. On the other hand, the Lynx, Wolf, 

 Fox, Grlutton, both Bears, Marten, Elk, Reindeer, Wapiti, Bison, Wild Sheep, 

 Beaver, Marmot, and some other N. -American forms, are either specifically 

 identical with Paloearctic animals or very nearly allied to them. Hesperomys 

 has been shown to be congeneric with Cricetus (Thomas, P. Z, S. 1888, p. 133). 

 In Central Asia are found several well-marked types, like Nectogale, Uropsilus, 

 Mluriis, Mluropus, Bicdorcas, Pantholops^ Poephagus, Moschus, and many others, 

 that distinguish the launa from that of the western Palsearctic area. 



In the case of Madagascar, not only are two mammalian families, ChiromyidcB 

 and Centetidce, and one subfamily, Cryptoproctince, peculiar to the island, but 

 out of about 24 genera of Primates, Carnivora, Insectivora, Eodentia, and 

 Ungulata found in Madagascar, and about 100 found in Africa south of the 

 Atlas, only two, Pofamochcerus and Crocidura, exist in both. The oriental 

 genera of the oi'ders mentioned are about 80 in number, and the Paltearctie 

 (omitting Seals) about the same ; of these about 30 are found in both regions. 

 Some 25 genera belonging to these orders are common to the Oriental and 

 Ethiopian areas, and 22 to the Paloearctic and Ethiopian, or to put the matter 

 more clearly, the African mammals comprise 25 per cent, of Oriental, 22 per 

 cent, of Paloearctic, and only 2 per cent, of Madagascar genera, whilst the 

 Madagascar forms comprise 8*3 per cent, of African genera. It must be 

 remembered that the climates of Madagascar and Tropical Africa are similar, 

 that of the Palaearc-tic region very different. 



Omitting New Zealand and Polynesia, the following appears to be the 

 division of the earth's surface into mammalian regions : — 



A. Mar.supials predominating ; placental mammals few ; monotremes 



present. 



I. Australian region, comprising, besides Australia and Tasmania, New 



Guinea, and the neighbouring islands east of Wallace's line. 



B. Placental mammals predominating; marsupials few or absent; no 



monotremes. 



II. South- American region. 



III. Arctogcean region, comprising the following major divisions: — 

 1. Madagascar. 



