404 
GEOGRAPHICAL ZOOLOGY. 
[part IV. 
liar ; and it has about 40 peculiar genera in ten families, about 
half of these genera belonging to the Scincidse. Only 3 
families of almost universal distribution are common to the 
Australian and Neotropical regions, with one species of the 
American Iguanidse in the Fiji Islands, so that, as far as this 
order is concerned, these two regions have little resemblance. 
The Neotropical region has 15 families, 6 of which are peculiar 
to it, and it possesses more than 50 peculiar genera. These are 
distributed among 12 families, but more than half belong to the 
Iguanidse, and half the remainder to the Teidse, — the two families 
especially characteristic of the Neotropical region. All the Ne- 
arctic families which are not of almost universal distribution are 
peculiarly Neotropical, showing that the Laeertilia of the former 
region have probably been derived almost exclusively from the 
latter. 
On the whole the distribution of the Laeertilia shows a 
remarkable amount of specialization in each of the great tropical 
regions, whence we may infer that Southern Asia, Tropical 
Africa, Australia, and South America, each obtained their original 
stock of this order at very remote periods, and that there has 
since been little intercommunication between them. The peculiar 
affinities indicated by such cases as the Lepidosternidse, found 
only in the tropics of Africa and South America, and Tachydromus 
in Eastern Asia and West Africa, may be the results either of 
once widely distributed families surviving only in isolated locali- 
ties where the conditions are favourable,— or of some partial and 
temporary geographical connection, allowing of a limited degree 
of intermixture of faunas. The former appears to be the more 
probable and generally efficient cause, but the latter may have 
operated in exceptional cases. 
Fossil Laeertilia. 
These date back to the Triassic period, and they are found in 
most succeeding formations, but it is not till the Tertiary period 
that forms allied to existing genera occur. These are at present 
too rare and too ill-defined to throw much light on the geo- 
graphical distribution of the order. 
