« EelmineJätka »
over the globe is not nearly so great as we might expect. This points to a long period of isolation, during which the various forms of life have acted and reacted on each other, leading to such a complex yet harmoniously-balanced result as to defy the competition of the chance immigrants that from time to time must have arrived. This is quite in accordance with the very high antiquity we have shown most insect-forms to possess; and it is no doubt owing to this antiquity, that such a complete diversity of generic forms has been here brought about, without any important deviation from the great family types which prevail over the rest of the globe.
Land Shells.—The Neotropical region is probably the richest on the globe in Terrestrial Mollusca, but this is owing, not to any extreme productiveness of the equatorial parts of the continent, where almost all other forms of life are so largely developed, but to the altogether exceptional riches of the West India Islands. The most recent estimates show that the Antilles contain more species of land shells than all the rest of the region, and almost exactly as many as all continental America, north and south.
Mr. Thomas Bland, who has long studied American land shells, points out a remarkable difference in the distribution of the Operculated and Inoperculated groups, the former being predominant on the islands, the latter on the continent. The Antilles possess over 600 species of Operculata, to, about 150 on the whole American continent, the genera being 'as 22 to 14. Of Inoperculata the Antilles have 740, the Continent 1,250, the genera being 18 and 22. The proportions of the two groups in each country are, therefore:
West India Islands.
American Continent. Operculata ... Gen, 22 Sp. 608 ...
18 , 737
22 1251 The extensive family of the Helicidæ is represented by 22 genera, of which 6 are peculiar. Spiraxis is confined to Central America and the Antilles ; Stenopus and Sagda are Antillean only; Orthalicus, Macroceramus, and Bulimulus have a wider range, the last two extending into the southern United
States. Important and characteristic genera are, Glandina, in all the tropical parts of the region; Cylindrella, in Central America and the Antilles ; Bulimus, containing many large and handsome species in South America; Stenogyra, widely spread in the tropics; and Streptaxis, in Tropical South America.
Among the Operculata, the Aciculidæ are mostly Antillean, two genera being peculiar there, and one, Truncatella, of wide distribution, but most abundant in the West Indian Islands. The Cyclostomidæ are represented by 15 genera, 9 being peculiar to the region, and 5 of these (belonging to the subfamily Licinidæ) to the Antilles only. Of these peculiar genera Cistula and Chondropoma are the most important, ranging over all the tropical parts of the region. Other important genera are Cyclotus and Megalomastoma ; while Cyclophorus also occurs all over the region. The Helicinidæ are mostly Neotropical, six out of the seven genera being found here, and four are peculiar. Stoastoma, is one of the largest genera; and, with Trochatella and Alcadia, is confined to the Antilles, while the wide-spread Helicina is most abundant there.
The Limacidæ, or Old World slugs, are absent from the region, their place being taken by the allied family, Oncidiadæ.
Marine Shells.—We go out of our usual course to say a few words about the marine shells of this region, because their distribution on the two sides of the continent is important, as an indication of the former separation of North and South America, and the connection of the Atlantic and Pacific Oceans. It was once thought that no species of shells were common to the two sides of the Central American Isthmus, and Dr. Mörch still holds that opinion; but Dr. Philip Carpenter, who has paid special attention to the subject, considers that there are at least 35 species absolutely identical, while as many others are so close that they may be only varieties. Nearly 70 others are distinct but representative species. The genera of marine mollusca are very largely common to the east and west coasts, more than 40 being so named in the lists published by Mr. Woodward. The West Indian Islands being a rich shell district, produce a number of peculiar forms, and the west coast of South America is, to some extent, peopled by Oriental and Pacific genera of shells. On the west coast there is hardly any coral, while on the east it is abundant, showing a difference of physical conditions that must have greatly influenced the development of mollusca. When these various counteracting influences are taken into consideration, the identity or close affinity of about 140 species and 40 genera on the two sides of the Isthmus of Panama becomes very important; and, combined with the fact of 48 species of fish (or 30 per cent. of those known) being identical on the adjacent coasts of the two oceans (as determined by Dr. Günther), render it probable that Central America has been partially submerged up to comparatively recent geological times. Yet another proof of this former union of two oceans is to be found in the fossil corals of the Antilles of the Miocene age, which Dr. Duncan finds to be more allied to existing Pacific forms, than to those of the Atlantic or even of the Caribbean Sea.
NEOTROPICAL SUB-REGIONS. In the concluding part of this work devoted to geographical zoology, the sub-regions are arranged in the order best adapted to exhibit them in a tabular form, and to show the affinities of the several regions ; but for our present purpose it will be best to take first in order that which is the most important and most extensive, and which exhibits all the peculiar characteristics of the region in their fullest development. We begin therefore with our second division.
II. Tropical South-America, or the Brazilian Sub-region. This extensive district may be defined as consisting of all the tropical forest-region of South America, including all the open plains and pasture lands, surrounded by, or intimately associated with, the forests. Its central mass consists of the great forestplain of the Amazons, extending from Paranaiba on the north coast of Brazil (long. 42° W.) to Zamora, in the province of Loja (lat. 4° S., long. 79° W.), high up in the Andes, on the west ;a distance in a straight line of more than 2,500 English miles, along the whole of which there is (almost certainly) one continuous virgin forest. Its greatest extent from north to south, is from the mouths of the Orinooko to the eastern slopes of the Andes near La Paz in Bolivia and a little north of Sta. Cruz de la Sierra (lat. 18° S.), a distance of about 1,900 miles. Within this area of continuous forests, are included some open“campos," or patches of pasture lands, the most important being,—the Campos of the Upper Rio Branco on the northern boundary of Brazil; a tract in the interior of British Guiana ; and another on the northern bank of the Amazon near its mouth, and extending some little distance on its south bank at Santarem. On the northern bank of the Orinooko are the Llanos, or flat open plains, partly flooded in the rainy season; but much of the interior of Venezuela appears to be forest country. The forest again prevails froin Panama to Maracaybo, and southwards in the Magdalena valley; and on all the western side of the Andes to about 100 miles south of Guayaquil. On the N.E. coast of Brazil is a tract of open country, in some parts of which (as near Ceara) rain does not fall for years together; but south of Cape St. Roque the coast-forests of Brazil commence, extending to lat. 30° S., clothing all the valleys and hill sides as far inland as the higher mountain ranges, and even penetrating up the great valleys far into the interior. To the south-west the forest country reappears in Paraguay, and extends in patches and partially wooded country, till it almost reaches the southern extension of the Amazonian forests. The interior of Brazil is thus in the position of a great island-plateau, rising out of, and surrounded by, a lowland region of ever-verdant forest. The Brazilian subregion comprises all this forest-country and its included open tracts, and so far beyond it as there exists sufficient woody vegetation to support its peculiar forms of life. It thus extends considerably beyond the tropic in Paraguay and south Brazil ; while the great desert of Chaco, extending from 25° to 30° S., lat. between the Parana and the Andes, as well as the high plateaus of the Andean range, with the strip of sandy desert op the Pacific coast as far as to about 5° of south latitude, belong to south temperate America, or the sub-region of the Andes.
Having already given a sketch of the zoological features of the Neotropical region as a whole, the greater part of which will apply to this sub-region, we must here confine ourselves to an indication of the more important groups which, on the one hand, are confined to it, and on the other are absent; together with a notice of its special relations to other regions.
Mammalia.Many of the most remarkable of the American monkeys are limited to this sub-region; as Lagothrix, Pithecia, and Brachyurus, limited to the great Amazonian forests; Eriodes to south-east Brazil ; and Callithrix to tropical South America. All the marmosets (Hapalidæ) are also confined to this sub-region, one only being found at Panama, and perhaps 'extending a little beyond it. Among other peculiar forms, are 8 genera of bats; 3 peculiar forms of wild dog; Pteronura, a genus of otters; Inia, a peculiar form of dolphin inhabiting the upper waters of the Amazon ; tapirs of the genus Tapirus (a distinct genus being found north of Panama); 4 genera of Muridæ ; Ctenomys, a genus of Octodontidæ; the whole family of Echimyidæ, or spiny rats, (as far as the American continent is concerned) consisting of 8 genera and 28 species ; Chætomys, a genus of Cercolabidæ; the capybara (Hydrochærus) the largest known rodent, belonging to the Caviidæ; the larger ant-eaters (Myrmecophaga); sloths of the genus Bradypus ; 2 genera of armadillos (Dasypodidæ); and two peculiar forms of the opossum family (Didelphyidæ). No group that is typically Neotropical is absent from this sub-region, except such as are peculiar to other single sub-regions and which will be noticed accordingly. The occurrence of a solitary species of hare (Lepus braziliensis) in central Brazil and the Andes, is remarkable, as it is cut off from all its allies, the genus not being known to occur elsewhere on the continent further south than Costa Rica. The only important external relation indicated by the Mammalia of this sub-region is towards the Ethiopian region, 2 genera of Echimyidæ, Aulacodes and Petromys, occurring in South and South-east Africa.
Plate IV. Characteristic Neotropical Mammalia.–Our illustration represents a mountainous forest in Brazil, the part of South America where the Neotropical Mammalia are perhaps best