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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 ai-e
distributed among 12 families, but more than half belong to the
Iguanidse, and half the remainder to the Teidee,—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 Lacertilia of the former
region have probably been derived almost exclusively from the
latter.
On the whole the distribution of the Lacertilia 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 Tachydromiis
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 Lacertilia.
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.