398 ZOOLOGICAL GEOGRAPHY. [PART III. 
The Australian region, then, possesses examples of 18 families 
of Mammalia, 8 of which are peculiar; 71 of Birds, 16 being 
peculiar; 31 of Reptiles, 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 
