Page:Encyclopædia Britannica, Ninth Edition, v. 20.djvu/488

Rh 470 REPTILES [GEOGRAl'IilrAL continent. The Chelonians of South America proper are the following (forty-three species) : Testudo, Emys, Cinosternum, Peltocephalus, Podocnemis, Platemys, Hydromedusa, Chelys, The Chclydidx thus predominate to the exclusion of the Emydidse. They belong to five distinct genera, of which one, Chehjs, is the most specialized of the family. They do not extend to the western side of the Andes, and cease in the south with the system of the Plate River. Northwards they penetrate to Trinidad, but become scarcer in the degree in which their place is occupied by the Emydidse, which have spread from Central America over the northern parts of this region. One, Emys cTorbignii, following the course of the Uruguay, has penetrated southwards to the mouth of the Plate River. Land Tortoises (Testudo) are at the present day almost extinct in this region, two species only (Testudo tabulate, or carbonaria and T. argentina) being found on the continent of South America. The six other species belong to the Oceanic Island Tortoises of gigantic size, and inhabit or inhabited the Galapagos group. Trionyx'ia entirely absent. The Crocodilian order is more developed in this region than in any other. Besides at least three species of Crocodilus, six Alligators occur. The former occupy Central America, with Mexico, the coast of Florida, the West Indies, Ecuador, and the system of the Orinoco ; the latter extend much farther southwards, throughout the system of the Plate River, whilst in North America this genus s> represented by a distinct species, A. missis- sipperisis. 1 Alligators found in some of the West Indian islands are believed to be immigrants from the continent. The Lacertilian fauna connects Central with South America, all the six families found in the latter area, viz., Geckonidaz, Anguidx, Amphisbxnidx, Tejidae, Igua- nidae, and Sdnddx, being represented in Central America. But Central America possesses, besides, five other families, small in species and restricted in range (some belonging to the fauna of great elevations), but highly interesting types. These are the JZublepharulas, Xenosauridse, Aniel- lid&, Helodermatidx, and Lepidophymatidas. Their locali- zation and differentiation can be accounted for on the hypothesis that they are the remains of the fauna of the various islands into which Central America was broken up at a former period. By far the larger number of Lizards of the Tropical American region are Iguanidie, a family which in the New World repeats the Old- World Agamidw. They are spread over the whole of the region, having adapted themselves in their mode of life and structure to every variety of ground. One species (Liolsemus magellanicus) ranges to the Straits of Magellan. The largest Iguanoids inhabit the Galapagos Islands, where they live on the rocks of the shore, one species (Oreocephalus cristatus) entering sea- water and feeding on sea-weeds. The next numerous family is the Tejidse, the New- World representatives of the Old- World Lacertidx ; Geckonidee, Scinddse, AmphisbsBnidee, and Anguidsz are less numerous, but have also a wide range over the region. The Lacertilian fauna of the West Indies is wholly South-American ; it does not comprise any peculiar family, and only a few character- istic genera, of which Anolisis, perhaps, the most highly specialized and the one which is composed of the greatest number of species ; this genus, however, is also well represented on the continent, especially in Central America. With regard to Ophidians the Tropical American region approaches the Indian in the number of species, which amounts to about four hundred, but it exhibits a com- paratively less variety of generic and peculiar forms ; of the eighty genera only about fifty do not range beyond its limits. However, a boundary line which would separate the Ophidian fauna of South America from that of the north does not exist. In Central America and 1 We may mention here, in anticipation, that a species of Alligator has recently been discovered in China. Mexico the generic types of the south and north are intermingled, and as the climate, in accordance with latitude and altitude, assumes a more temperate character the specifically tropical Snakes disappear and arc in part replaced by those of North America. This mixture of the two faunai and the great variety of physical conditions within a small area account for the relatively very large number of Snakes of Central America. About one hundred and fifty out of the four hundred species attri- buted to the whole region belong to this district. The West- Indian Ophidians belong to the Tropical American fauna ; many continental generic forms of the latter occur in the islands, and such genera as are peculiar to the West Indies do not exhibit a common feature, or are founded on slight characters. The exact limits to which Snakes extend southwards are not known ; they seem to be very scarce on the southern confines of the Argentine Republic. Quite recently a Crotaline Snake, Rhinocerophis, has been discovered in eastern Patagonia. 2 Of families peculiar to or highly characteristic of this fauna we can mention one only, viz., the small family Scytalidae, which replaces the Lycodonts of the Old World. The JBoidx are likewise a prominent feature, although not exclusively confined to South America ; of eleven genera eight are Tropical American, and three Australian. The true Boas include the most gigantic of Snakes, and replace the Old- World Pythons. In this fauna a peculiar and highly ornamental pattern of coloration, which consists of more or less regularly alternate rings of black, red, and yellow, seems to be the more worthy of notice, as it occurs in very distinct families, viz., the Ccdamariidx, Coronellidx, Natriddx, Leptognath- idse, Scytalidse, Tortricidee, Elapidx. Of TyjMopidae, more than twenty species have been described, and, besides, the Stenostomatidse, are represented by seven species. Of Tortricidse one species occurs. The Calamariid& are represented by thirteen genera, of which ten are peculiar. The most characteristic and geographically important are Elapomorphus with ten, Humalocranium with sixteen, Ninia with four species. The Indian genus GeopJn's is represented in Tropical America by twenty-five species. CoronellidsR are extremely numerous (sixty-six species referable to thirteen genera). Of these Xenodon with twelve species, Lio- pliis with sixteen, JErythrolamprus, and Pliocercus deserve special mention. Of Colubers forms with elongate compressed body, approaching arboreal forms (Spilotcs), are not scarce. Freshwater Snakes are not abundant, but a genus peculiar to the region, Hclicops, occurs in eight species. Tropidonotus might be regarded as absent, but for three or four species which occur north of the Isthmus of Panama and in the West Indies ; also the allied genus Tretanorhimis is confined to Central America and the West Indies. Tree Snakes are extremely abundant some seventy species refer- able to six gen era, of which Dromicus, Philodryas, and Hcrpetodryas are very characteristic forms. Of Ah&tulla some seventeen species are known. Of Dipsas and allied genera only four species occur, but of the peculiarly South-American Lepioynathidaz some twenty-five spivii-s have been distinguished. In Central America there occur two extremely singular forms which, however, are imperfectly known and seem to be restricted to a very limited area. One, Loxocemus, is considered a representa- tive of the family Pythonidse, and the other, Notopsis, is stated to be the type of a distinct family allied to the Indian Xcnodcnnid. Of the twenty species of fioidse the West Indian contingent amounts to no less than eight or nine, a fact which clearly demonstrates the pertinence of the West Indies to this region. Eryeidie are absent Poisonous Snakes are numerous, the proportion to innocuous Snakes being as 1 : 8. Besides the singular occurrence in Venezuela of a member of the Atraetaspididie, Dinodipsas, the Colubriform poisonous Snakes are represented by one genus only, EJcps, which, however, shows numerous varieties or species, and is extremely common and widely spread over the region. Vlperida arc aWnt ; but the largest forms of Pit Vipers (Crotalidse) arc developed in this 2 There is reason to believe that Euophrys, which has been placed among the Psamtnophidee,, is likewise a Patagonian form.