Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/485

DISTRIBUTION.] REPTILES 467 They are much specialized in their mode of life and pro- pagation, and ill adapted to accommodate themselves to a change of external conditions. As air-breathing cold- blooded animals they are unable to withstand prolonged cold ; they are therefore entirely absent in the arctic and antarctic zones ; and such as escape the effect of the winter months in temperate zones by passing them in a torpid condition in well-sheltered places are not peculiarly organized forms, but offshoots from those inhabiting warmer climes. The tropical and subtropical zones are the real home of the Eeptilian type, which there has reached its greatest development as regards size and variety of forms. In the north Chelonians advance only to 50 lat. in the western and to 56 in the eastern hemisphere, Lizards to about 56 in British Columbia, and close to the Arctic Circle in Europe, whilst Snakes disappear some degrees before the Lizards. Also in the south Lizards extend into higher latitudes than Snakes, viz., to the Straits of Ma- gellan, whilst the latter do not seem to have advanced beyond 40 S. lat. and Chelonians only to 36. We exclude from our account of the distribution of terrestrial Reptiles those few forms which pass almost the whole of their life in the sea, and therefore belong to the marine faunae, viz., the Marine Turtles and Sea-Snakes. 1. The shores of the continents and islands of the equatorial zone are the home of the Marine Turtles. Endowed with a wonderful power of locomotion, the several species are now distri- buted over the greater part of this zone, occurring in the Atlantic as well as the Indo-Pacific ; and, although some of them are common in certain districts and scarcer or even absent in others, it is pro- bable that in the course of time their distribution will be still more general and uniform, as far as other conditions (such as access to a suitable locality for the successful propagation of their kind) will permit. Frequently Marine Turtles stray far into the temperate zones, and it thus happens that one and the same species (Sphargis coriacea) has been found on the south coast of England, near Cape Cod in North America, and on the coast of Chili. In short the geographical distribution of these Reptiles is that of pelagic animals generally, although by their mode of pro- pagation they are compelled to sojourn near land during a certain period of the year. 2. The Sea-Snakes are restricted to, and highly characteristic of, the fauna of the tropical Indo-Pacific Ocean, and more especially of parts between Arabia and North Australia. They prefer the vicinity of laud, but never leave the water, with, perhaps, the single exception of Platurus. Their distribution is not erratic; only one species, Pelamys bicolor, a Sea-Snake which more than any other is organized for a marine life, has spread far beyond the original home of its kindred, viz., westwards to the coasts of Madagascar and south-eastern Africa, and eastwards to the further- most limits of the region, viz., to the coasts of central and northern South America. All other Reptiles 1 are terrestrial, and, as they are chiefly developed in the tropics, we begin our account with the regions 2 of the equatorial zone. The scope of this article does not allow us to enter into an examination of the subregions which have been proposed by various authors. 1. The Indian Region. Of the four principal groups of terrestrial Chelonians, the Emydidse, and Trionycidae (Freshwater Tortoises and Freshwater Turtles) predomi- nate over the Testudinidse, which are scarce and restricted, the fourth (Chelydidse) being absent altogether. We know fifty-seven species from this region : Testudo, 4 species Manouria, 1 Cistudo (Cuora), 3 Emys with its subgenera, 30 Platysternum, 1 Trionyx, 15 Emyda, 3 IS 1 The fact that Oreocepholus enters the sea habitually and Cher- sydrus frequently does not entitle these Reptiles to be classed among marine animals ; they pass the greater part_of their life on land, and never leave its close vicinity. 2 As regards the general boundaries of the zoo-geographical regions we refer to Wallace's Geographical Distribution of Animals (London, 1870, 4to) or to the article ICHTHYOLOGY (vol. xii. pp. 668 sq.). Three of these genera are peculiar to the region, viz., Manouria, 3 Platysternum, and Emyda. Characteristic is the scanty repre- sentation of Testudo. One species which is common in the Indian peninsula ( T. stellata) is so similar to an African species as to have been considered identical with it ; the Burmese Tortoise is also closely allied to it, and the two others extend far into western Central Asia. Thus this type is to be considered rather an immi- grant from its present headquarters, Africa, than a survivor of the Indian Tertiary fauna, which comprised the most extraordinary forms of Land Tortoises. Wallace's line marks the eastern bound- ary of Trionyx ; species "of this genus are common in Java and Borneo, and occur likewise in the Philippine Islands, but are not found in Celebes, Amboyna, or any of the other islands east of Wallace's line. 4 Of Crocodilidss true Crocodiles are represented by four, Croco- and Gavials by two species. Alligators are absent. dilians. Although the region is characterized by numerous highly Lacer- specialized genera of Lacertilia, not one of the families is tilian s. peculiar to it. Agamidas are exceedingly numerous, and are represented chiefly by arboreal forms ; terrestrial forms, like Agama and Uromastix, inhabit the hot and sandy plains in the north-west, and pass unin- terruptedly into the fauna of western Central Asia and Africa. The Geckonidse, Scincidse,, and Varanidx are likewise well repre- sented, but without giving a characteristic feature to the region by special modification of the leading forms. The Lacertidas are repre- sented by one characteristic genus, Tachydromus, Ophiops and Cabrita being more developed beyond the limits assigned to this region. Finally, the Eublcpliaridx and Anguidse, families whose living representatives are probably the scattered remains of once widely and more generally distributed types, have retained respec- tively two species in western India, and one in Khassia (Khasi Hills), whilst the presence of a single species of Chamseleon in Southern India and Ceylon reminds us again of the relations of this part of the fauna to that of Africa. The Indian region excels all the other equatorial regions Ophi- in the great variety of generic types and number of dians. species of Snakes. The latter amount to no less than four hundred and fifty, which is nearly one-third of the total number of species known. They are referable to about one hundred genera, of which the majority do not range beyond the limits of the region. Of higher groups (termed families for the sake of convenience), the Xenopeltidse, Rhinophidse, Oligodontidse, Xenodermidx, and Acrochordidss are peculiar to, and characteristic of, this fauna, but not more so than a number of genera which will be mentioned presently. Of Typhlopidse, more than twentj' species are known. Of Tortricidee, the genus Cylindrophis is spread over several if the subregions. The Calamariidie are represented by a whole string of genera, of which thirteen are peculiar to the region. The most characteristic and geographically most important types are Calamaria, with twenty-four species, spread over the archipelago and the eastern parts of the continent, and Aspidura and Haplocercus, with four species, which are limited to Ceylon and southern India. Species of those generalized forms which are termed Coronellidte and Colubridx are likewise numerous (sixty-six species), and referable to seventeen genera, of which ten are limited to this region. In the north-western and northern parts the genus Zamenis, which is one of the most characteristic types of the warmer parts of the Europe-Asiatic fauna, is represented by six species. Freshwater Snakes are abundant in genera,-species, and indivi- duals. Of Tropidonotus alone some forty very distinct species have been described, besides three others which are sufficiently differen- tiated to deserve generic separation. Of the so-called Homalopsidse all the genera, twelve in number, are peculiar, and the great development of these Snakes is, therefore, one of the most striking features of this region. Besides two species of Psammophis allied to African forms, a dis- tinct genus Psammodynastes has a wide range over the eastern parts of the continent and the archipelago. Tree Snakes are represented by eight genera and twenty-six species, mostly characteristic forms. 3 Its existence in Australia is extremely doubtful. 4 The statement that specimens of Trionyx had been obtained by Ida Pfeiffer in Amboyna rests upon a misunderstanding, like that of the discovery of a Barbel by the same traveller in the same island. Dr Jentink also informs us :hat none of the Freshwater Turtles in the Leyden Museum came froir islands east of Java and Borneo.