398 ZOOLOGICAL GEOGRAPHY. [part hi. 



The Australian region, then, possesses examples of 18 families 

 of Mammalia, 8 of which are peculiar ; 71 of Birds, 16 being 

 peculiar; 31 of Eeptiles, 4 being peculiar ; 11 of Amphibia, with 

 1 peculiar; and 11 of Fresh-water fish, with 1 peculiar. In all, 

 142 families of Vertebrates, 30 of which are almost or quite 

 confined to it, or between one-fourth and one-fifth of the whole 

 number. 



The genera of Mammalia, occurring within the limits of this 

 region are 70, of which 45 are almost, or quite, confined to it. 



Of Land-Birds there are 296 genera, 196 of which are equally 

 limited. The proportion is in both cases very nearly five- 

 eighths. 



This shows a considerable deficiency both in families of Ver- 

 tebrates and genera of Mammalia, as compared with the Oriental 

 and Ethiopian regions ; while in genera of Birds it is a little 

 superior to the latter in total numbers, and considerably so in 

 the proportion of peculiar types. 



Supposed Land Connection between Australia and South America. 



We may now consider how far the different classes and orders 

 of vertebrates afford indications that during past ages there 

 has been some closer connection between Australia and South 

 America than that which now exists. 



Among Mammalia we have the remarkable fact of a group 

 of marsupials inhabiting South America, and extending even 

 into the temperate regions of North America, while they are 

 found in no other part of the globe beyond the limits of the 

 Australian region ; and this has often been held to be evidence 

 of a former connection between the two countries. A prelimi- 

 nary objection to this view is, that the opossums seem to be 

 rather a tropical group, only one species reaching as far as 42° 

 south latitude on the west coast of South America ; but what- 

 ever evidence we have which seems to require a former union 

 of these countries shows that it took place, if at all, towards their 

 cold southern limits, the tropical faunas on the whole showing 

 no similarity. This is not a very strong objection, since climates 

 may have changed in the south to as great an extent as we 



