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is in peculiar types of all the most characteristic American families, such as the Tanagridae, Tyrannidae, Cotingidae, Formicariidae, Trochilidae, and Galbulidae. A considerable proportion of the genera of the Chilian and Mexican sub-regions also occur here, so that out of about 680 genera of Neotropical landbirds more than 500 are represented in this sub-region.
Without entering minutely into the distribution of species it is difficult to sub-divide this extensive territory with any satisfactory result1 The upland tract between the Amazon and Orinooko, which may be termed Guiana, was evidently once an island, yet it possesses few marked distinctive features. Brazil, which must have formed another great island, has more speciality, but the intermediate Amazonian forests form a perfect transition between them. The northern portion of the continent west of the Orinooko has more character; and there are indications that this has received many forms from Central and North America, and thus blended two faunas once more distinct than they are now. The family of wood-warblers (Mniotiltidae) seems to have belonged to this more northern fauna; for out of 18 genera only 5 extend south of the equator, while 6 range from Mexico or the Antilles into Columbia, some of these being only winter immigrants and no genus being exclusively South American. The eastern slopes of the Andes constitute, however, the richest and best marked province of this sub-region. At least 12 genera of tanagers (Tanagridae) are found here only, with an immense number of Fringillidae,—the former confined to the forests, the latter ranging to the upland plains. The ant-thrushes (Formicariidaj) on the other hand seem more abundant in the lowlands, many genera being peculiar to the Amazonian forests. The superb chatterers (Cotingidae) also seem to have their head-quarters in the forests of Brazil and Guiana, and to have thence spread
1 Messrs. Sclater and Salvin, and Professor NewtoD, divide the Neotropical Region into six sub-regions, of which our " Brazilian sub-region" comprises three—the "Brazilian," the "Amazonian," and the "Columbian ;" but, after due consideration, it does not seem advisable to adopt this subdivision in a general work which treats of all the classes of terrestrial animals. (See p. 27.)
into the Amazonian valley. Guiana still boasts such remarkable forms as the cardinal chatterer (Phcenicocercus), the military chatterer (Hcematoderus), as well as Querula, Gymnoderus, and Gymnocephalus; but the first three pass to the south side of the Lower Amazon. Here also belong the cock of the rock (Rupicola), which ranges from Guiana to the Andes, and the marvellous umbrella-birds of the Rio Nigro and Upper Amazon (Cephalopterus), which extends across the Ecuadorean Andes and into Costa Rica. Brazil has PtUochloris, Casiornis, Tijuca, Phibalura, and Calyptura; while not a single genus of this family, except perhaps Heliockcera, is confined to the extensive range of the Andes. Almost the same phenomena are presented by the allied Pipridee or manakins, the greater part of the genera and species occurring in Eastern South America, that is in Brazil, Guiana, and the surrounding lowlands rather than in the Andean valleys. The same may be said of the jacamars (Galbulidse) and puff-birds (Bucconidse); but the humming-birds (Trochilidae) have their greatest development in the Andean district. Brazil and Guiana have each a peculiar genus of parrots; Guiana has three peculiar genera of Cracidse, while the Andes north of the equator have two. The Tinamidse on the other hand have their metropolis in Brazil, which has two or three peculiar genera, while two others seem confined to the Andes south of the equator. The elegant trumpeters (Psophiidse) are almost restricted to the Amazonian valley.
Somewhat similar facts occur among the Mammalia. At least 3 genera of monkeys are confined to the great lowland equatorial forests and 1 to Brazil; Icticyon (Canidae) and Pteronura (Mustelidae) belong to Guiana and Brazil; and most of the Echimyidae are found in the same districts. The sloths, anteaters, and armadillos all seem more characteristic of the eastern districts than of the Andean; while the opossums are perhaps equally plentiful in the Andes.
The preceding facts of distribution lead us to conclude that the highlands of Brazil and of Guiana represent very ancient lands, dating back to a period long anterior to the elevation of the Andean range (which is by no means of great geological antiquity) and perhaps even to the elevation of the continuous land which forms the base of the mountains. It was, no doubt, during their slow elevation and the consequent loosening of the surface, that the vast masses of debris were carried down which filled up the sea separating the Andean chain from the great islands of Brazil and Guiana, and formed that enormous extent of fertile lowland forest, which has created a great continent; given space for the free interaction of the distinct faunas which here met together, and thus greatly assisted in the marvellous development of animal and vegetable life, which no other continent can match. But this development, and the fusion of the various faunas into one homogeneous assemblage must have been a work of time; and it is probable that most of the existing continent was dry land before the Andes had acquired their present altitude. The blending of the originally distinct sub-faunas has been no doubt .assisted by elevations and depressions of the land or of the ocean, which have alternately diminished and increased the land-area. This would lead to a crowding together at one time, and a dispersion at others, which would evidently afford opportunity for many previously restricted forms to enter fresh areas and become adapted to new modes of life.
From the preceding sketch it will appear, that the great subregion of Tropical South America as here defined, is really formed of three originally distinct lands, fused together by the vast lowland Amazonian forests. In the class of birds sufficient materials exist for separating these districts; and that of the Andes contains a larger series of peculiar genera than either of the other sub-regions here adopted. But there are many objections to making such a sub-division here. It is absolutely impossible to define even approximate limits to these divisions—to say for example where the "Andes" ends and where "Brazil" or "Amazonia" or "Guiana" begins; and the unknown border lands separating these are so vast, that many groups, now apparently limited in their distribution, may prove to have a very much wider range. In mammalia, reptiles, and insects, it is even more difficult to maintain such divisions, so that on the whole it seems better to treat the entire area as one sub-region,