Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/487

Rh DISTBIBUTJON.] KEPTILES 469 la- tis of 1 lea to lia. opical .ciftc nans. Africa : no Trionyx occurs in Madagascar. On the other hand species are found of Tesludo, Chersinc, Sternothcrus, and Pelomedusa, which are spread also over a greater or lesser area of the continent. Two Chelonians, Pyxis and Dumerilia, are peculiar to Madagascar, the latter nearly allied to the South -American Peltocephalus. The Madagascar Crocodile is closely allied to the common African species.; and its presence in the island can be easily accounted for. Among the Lizards we find a distinctly South-American element in two Iguanoid genera, Hoplurus and Chalarodon, replacing the Old World Agamidss. The absence of Vamnidaz, Locerlidee, and AmpltisbiRnidee, removes Madagascar from Africa, whilst the extra- ordinary development of Cham&lconidse (more than twenty species) and the presence of Gerrhosauridas and Zonuridae, are important features common to both. A very small family (Uroplatidse) is peculiar to Madagascar. No special relation to the Indian region is shown by this Lacertilian fauna. With regard to Ophidians, Madagascar has hardly anything in coiumon with Africa. The African fauna is characterized by the great development of Lycodonts, they are absent in Madagascar ; and of the four families of African poisonous Snakes Madagascar does not possess a single one. When we analyse the affinities of the twenty-seven species known at present from Madagascar, we arrive at the following conclusions : 1. Snakes without distinct relations to any particular region : Typhlops (six species), Ablabes (one species), Ithycyphus (one species), Dipsadoboa (one species). 2. Snakes with affinities to the African fauna : Mimophis (one species), Pelaphilus (one species). 3. Snakes with affinities to the Indian fauna : Ptyas (one species), Langaha (one species). 4. Snakes with affinities to the South-American fauna : Liophis (one species), Tachymenis (one species), Pseudoxyrhopus (two species), Heterodon (two species), Dromicus (one species), Herpeto- dryas (one species), Philodryas (one species), Dipsas (two species), Xiphosoma (one species). Africa shows affinities to all the three other equatorial regions, but chiefly to the Indian. No sharply defined boundary exists between the two regions, the intervening parts of Asia being inhabited by a desert fauna which penetrates into districts of similar nature in Africa as well as in India. Certain genera and species belonging to this desert fauna are therefore common to both regions. But there are, besides, other points of affinity of deeper signifi- cance, such as the development in both of a distinct Trionycoid genus, besides the typical Trionyx, the general distribution of Agamoids and Varanidse, 1 the presence of the remarkable family of Lycodonts, which do not occur anywhere else, of the large forms of Python with con- comitant absence of Booids, and of the Elapidx, of which one genus (Najci) extends from the west coast of Africa to Borneo. But these resemblances are fully counterbalanced by great differences in other portions of the Reptilian fauna : the Indian Emydoids are replaced by Chelydidse in Africa, a type which it has in common with Australia and South America, whereas India possesses no Amphisbsenidse, no Chamaeleons. 2 With regard to Ophidians, the number of forms generally is greatly diminished in Africa, but the proportion of poisonous Snakes is doubled. The Pit Vipers of India are wholly absent, and are replaced by true Vipers. In the Indian region arboreal Agamoid Lizards prevail ; in Africa the Snakes show a greater tendency towards a modification of the habitus and structure for arboreal life. The Freshwater Snakes and Colubers which are so numerous in India are much reduced in numbers in Africa, Tropidonoti being almost entirely absent. 3. The Tropical Pacific Region. So far as Reptiles are concerned, Tasmania has to be included in this region. No Trionyx or Emys goes eastwards beyond Wallace's line. In fact, the Chelonian type disappears in the islands between this line and the Australian continent with two exceptions. A species of Tesludo (T. forstenii) occurs in, and is limited to, the island of Gilolo ; and 1 Both these Lacertilian families extend into the Australian region ; in fact they replace the Iguanoids of the western hemisphere and Madagascar. 2 With the single exception mentioned nbove. Cuora amboinensis, the most common Tortoise of Malaya, occurs in many of the eastern islands, but it has probably been imported by man, and by the same means may be still extending its range. On the continent of Australia Chelydidx only occur, viz., eight species of Chelemys and five of CJielodina. In Tasmania, again, Chelonians are absent. Besides the common Indian Crocodilus porosw, which Croco- may be considered an immigrant into this region, one or Lilians, two other species of the same genus inhabit the fresh waters of the truly tropical parts, and are peculiar to Australia. The bulk of the Lacertilian fauna is composed of Skinks, Lacer- Geckos, Agamoids, and Varanidse, with the addition of a tilians. small family which is peculiar to the region, the Pygo- podidse. A peculiar type, Dibarmts, has been found in New Guinea; and, finally, a single Iguanoid, Brachylophus, is common in the Fiji Islands ; how it came there, or how it survived its severance from the American stock, is a mystery. The Skinks are in this region more highly developed and more specialized than in any other part of the world; they exceed in numbers the Geckos, which generally accompany the Skinks in their range over the smaller islands of the Pacific; in these islands members of these two families represent the whole of the Lacer- tilian fauna. The Australian Agamoids are chiefly peculiar and partly much differentiated forms, but some have distinct affinities to, or are even identical with, Indian genera. The Varanidse are also closely allied to Indian species. The total number of Snakes amount to ninety species, Ophi- of which twelve are Typhlops, eight other innocuous dians. Colubrines, fifty Elapidse, one Erycine, fourteen Pythonidx, and five Boidse. The number of poisonous Snakes, there- fore, exceeds that of innocuous, a proportion quite un- paralleled in any other part of the world. The few innocuous Colubrine Snakes belong to Indian genera, and evidently have spread from that region ; but all the genera of Elapidx (twelve), Erycidee, (one), Pythonidy (five), and Boidx (three) are peculiar to this region. In Australia we meet, therefore, with the interesting fact that, whilst it is closely allied to South America, but totally distinct from India, by its Chelonians, its Lizards and Colubrine Snakes connect it with this latter region. With regard to the other Ophidians, they, although peculiar genera, have their nearest allies partly in India ] tartly in South America; and the character of the Australian Snake fauna consists chiefly in its peculiar composition, differing thereby more from the other equatorial regions than these do among themselves. Wallace's line marks the boundary between India and Australia only as far as Chelonians are concerned, but it is quite effaced by the distribution of Lizards and Snakes. Thus in New Guinea Lizards of the Indian region are mixed with Pygojwdidss, and an island as far east as Timorlaut is inhabited by six Snakes, three of which are peculiarly Indian, whilst the other three are as decidedly Australian. The islands north of New Guinea and of Melanesia are not yet occupied by the Ophidian type, and only species of Enygrus have penetrated eastwards as far as the Low Archipelago, whilst the Fiji Islands and the larger islands of Melanesia have sufficiently long been raised above the level of the sea to develop quite peculiar genera of Snakes. Tasmania is tenanted by poisonous Snakes only. 4. The Tropical American Region. An examination of Tropical the distribution of Chelonians in the New World leads to America a different division of its regions from that of the other Q^ n ' Reptiles. Central America and the West Indies, withi om - ans> regard to Chelonians, cannot be united with the Southern