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liar; and it has about 40 peculiar genera in ten families, about half of these genera belonging to the Scincidae. Only 3 families of almost universal distribution are common to the Australian and Neotropical regions, with one species of the American Iguanidae 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 Iguanidae, and half the remainder to the Teidae, the two families especially characteristic of the Neotropical region. All the Nearctic 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 Lepidosternidae, 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 localities 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 geographical distribution of the order.
The singular and isolated genus Hatteria—the “Tuatara” or fringed lizard—which alone constitutes this family, has peculiarities of structure which separate it from both lizards and crocodiles, and mark it out as an ancestral type, as distinct from other living reptiles as the Marsupials are from other Mammalia. It is confined to New Zealand, and is chiefly found on small islands near the north-east coast, being very rare, if not extinct, on the main land. A fossil reptile named Hyperodapedon, of Triassic age, has been found in Scotland and India, and is supposed by Professor Huxley to be more nearly allied to Hatteria than to any other living animal.
The Gavials are long-snouted Crocodiles with large front teeth, and canines fitting in notches of the upper jaw. They consist of two genera, Gavialis (1 sp.), inhabiting the Ganges; Tomistoma (2 sp.), found in the rivers of Borneo and North Australia.
The true Crocodiles, which have the canines in notches, and the large front teeth in pits in the upper jaw, are widely distributed over the tropical regions of the globe, inhabiting all the rivers of Africa, the shores and estuaries of India, Siam, and eastward to North Australia. Other forms inhabit Cuba, Yucatan, and Guatemala, to Ecuador and the Orinooko. Four species are Asiatic, one exclusively Australian, three African, and four American. These have been placed in distinct groups, but Dr. Günther considers them all to form one genus, Crocodilus.
The Alligators, which are distinguished by having both the large front teeth and the canines fitting into pits of the upper jaw, are confined to the Neotropical, and the southern part of the Nearctic regions, from the lower Mississippi and Texas through all Tropical America, but they appear to be absent from the Antilles. They are all placed by Dr. Günther in the single genus, Alligator.
General Remarks on the Distribution of Crocodilia.
These animals, being few in number and wholly confined to the tropical and sub-tropical regions, are of comparatively little interest as regards geographical distribution. America possesses both Crocodiles and Alligators; India, Crocodiles and Gavials; while Africa has Crocodiles only. Both Crocodiles and Gavials are found in the northern part of the Australian region, so that neither of . the three families are restricted to a single region.
The existing families of the order date back to the Eocene period in Europe, and the Cretaceous in North America. In the south of England, Alligators, Gavials and Crocodiles, all occur in Eocene beds, indicating that the present distribution of these families is the result of partial extinction, and a gradual restriction of their range—a most instructive fact, suggesting the true explanation of a large number of cases of discontinuous distribution which are sometimes held to prove the former union of lands now divided by the deepest oceans. In more ancient formations, a number of Crocodilian remains have been discovered which cannot be classed in any existing families, and which, therefore, throw no light on the existing distribution of the group.
The Testudinidae, including the land and many fresh-Water tortoises, are very widely distributed over the Old and New worlds, but are entirely absent from Australia. They are especially abundant in the Nearctic region, as far north as Canada and British Columbia, and almost equally so in the WOL. II.—27
Neotropical and Oriental regions; in the Ethiopian there is a considerable diminution in the number of species, and in the Palaearctic they are still less numerous, being confined to the warmer parts of it, except one species which extends as far north as Hungary and Prussia. The genera are:— . . . . . Testudo (25 sp.), most abundant in the Ethiopian region, but also extending over the Oriental region, into South Europe, and the Eastern States of North America; Emys (64 sp.), abundant in North America and over the whole Oriental region, less so in the Neotropical and the Palaearctic regions; Cinosternon (13 sp.), United States and California, and Tropical America; Aromochelys (4 sp.), confined to the Eastern States of North America; Staurotypus (2 sp.), Guatemala and Mexico; Chelyāra (1 sp.), Canada to Louisiana; Claudius (1 sp.), Mexico; Dermatemys (3 sp.), South America, Guatemala, and Yucatan; Terrapene (4 sp.), Maine to Mexico, Sumatra to New Guinea, Shanghae and Formosa—a doubtfully natural group; Cinyasis (3 sp.), Pyasis (1 sp.), Chersina (4 sp.), are all Ethiopian ; Dumerilia (1 sp.), is from Madagascar only.
The Chelydidae, or fresh-water tortoises with imperfectly retractile heads, have a remarkable distribution in the three great southern continents of Africa, Australia, and South America; the largest number of species being found in the latter country. The genera are:—
Peltocephalus (1 sp.), Podocnemis (6 sp.), Hydromedusa (4 sp.), Chelys (1 sp.), and Platemys (16 sp.), inhabiting South America from the Orinooko to the La Plata, the latter genus occurring also in Australia and New Guinea; Chelodina (5 sp.), Chelemys (1 sp.), and Elseya (2 sp.) from Australia; while Sternotheres