natural boundaries. Neglect of these indications has led to much of the difference of opinion in the question of geographical distribution, which have been founded principally on the conditions presented by the birds and mammalia. In this system fragments of existing or old continents, which have been subjected to conditions unfavorable to particular forms of life otherwise prevalent in them, are, as in the system of Sclater, disregarded. Thus, islands generally are not regarded as presenting conditions definitive of divisions of the first rank, as was done by Huxley and Gill in the case of New Zealand, and Gill and Lydekker in the Polynesian Islands. The temperate regions of Africa and South America are certainly not separable from the tropical portions, as divisions of primary rank, as was done by Allen, who is followed as to South America by Gill. With equal propriety western North America might be separated from Mississippi and Atlantic North America, on account of the great deficiency of its fish fauna. In estimating faunistic affinities one has to give similarities over a given area more weight than differences, where the differences are only due to absence of types. Finally, it must be remembered that there are geographic points of transition between all the realms. I. THE ARCTOGEAN REALM. This realm includes three regions, viz. : the Indian, the Holarctic and the Medicolumbian. I have already defined the first two in general terms. The third is the transitional of Heilprin, the Sonoran of Merriam and Lydekker, and the Neotemperate of Townsend. It embraces what is left of the Nearctic of Sclater after the subtraction of the Holarctic. As the name Sonoran has been previously given by me to one of the districts of this region, I have preferred to use for it the name given by Blanford. The faunal characteristics of these regions may be enumerated af follows: Indian Region.-Presence of Holostomatous fishes. Absence of Ginglymodous and Halecomorphous and Salmonid fishes. Presence of Coeciliid Batrachia. Absence of Trachystomatous, Amphiumid, Cyptobranchid, and Arciferous Batrachia. Presence of Agamid lizards, and Anigiostomatous and Viperid snakes. Presence of Phasianid, Eurylamid, Nectariniid and Pittid birds. Absence of Tyrannid and of several nine-quilled oscine families. Presence of nomarthrous Edentata, of Viverridæ, Hyænidæ, Tupæidæ and Tarsiida. Presence of Rhinocerotida, Tapiridæ, Proboscidia, and Catarrhine Quadumana, and Anthopomorpha. Absence of Didelphyidæ, Procyonidæ and Scalopidæ. Holarctic Region.-Absence of Holostomatous and Halecomorphous fishes. Presence of Ginglymodous and Salmonid fishes. Absence of Trachystomatous, Amphiumid and Coeciliid Batrachia, and absence of the Arcifera except the family Discoglossidæ (two species of Hyla excepted). Absence of Angiostomatous and presence of Viperid snakes. Presence of Phasianid, and absence of Eurylamid, Nectariniid, Pittid and Tyrannid birds, and of several nine-quilled oscine families or subfamilies. Absence of Nomarthrous Edentata, of Viverridæ, Hyænidæ, Tupæidæ, Rhinocerotidæ, Tapiridæ, Proboscidia, Quadrumana and Anthropomorpha (except Homo). Medicolumbian Region.-Absence of Holostomatous fishes; presence of Ginglymodous and Halecomorphous fishes. Presence of Trachystomatous, Amphiumid, Aciferous and Firmisternial Batrachia, and absence of Coeciliida. Presence of Iguanid, and absence of Agamid and Chamæleonid lizards; absence (except three species) of Angiostomatous and of Viperid snakes. Absence of the Indian types of Passeres mentioned, and presence of Tyrannid Clamatores, and several groups of nine-quilled Oscines (Icterida Mniotiltidæ, Tanagridae). Absence of all the specially Indian mammalia, and of the Holarctic Erinaceidæ, and presence of Didelphyidae (one species), Scalopidæ and Procyonidæ. In defining these regions I have restricted myself necessarily to types of tolerably high rank, and have not referred to species. This is because species are not generally characteristic of entire divisions, but only of parts of them. One cannot, however, be absolutely exact in such major definitions, since a number of the conspicuous types in each are not universally distributed over these areas. In comparing the Holarctic with other realms, I have already referred to the number of types which it possesses in common with the Ethiopian, not found in the Neotropical. It has also several in common with the Neotropical, which do not occur in the Ethiopian. These are the Arciferous Batrachia, the Crotalid snakes, and the deer (Cervidae). The Medicolumbian division of the Holarctic shares other forms with the Neotropical. These are Didelphyidæ and Procyonidæ among Mammalia; Tyrannid, Icterid and Tanagrid birds; Kinosternid tortoises and the Arciferous Batrachian family Hylidæ. Some of the forms of the Holarctic region are not uniformly distributed over it. Thus the Ginglymodous and Spatulariid fishes only occur in the eastern parts of the eastern and western continents. The same is true of the Silurid genus Amiurus and the Loricate genus Alligator. The Crotalid snakes are not found in the western parts of Eurasia. The Batrachian Cryptobranchidæ have the same distribution. II. THE MEDICOLUMBIAN REGION. This region was formerly included in the Nearctic of Sclater, and the area thus constituted has the following geographic boundaries. To the south it includes the plateau of Mexico, including the central valley. The Neotropical area bounds it to the east and west, occupying the low-lands or Tierra Caliente to a point 150 miles south of the Rio Grande on the east, (Townsend, Texas Academy of Science, 1895, p. 87), and to Mazatlan, or some point not far from it, on the west. The high land of Oaxaca is its extreme southern outpost. Its northern boundary is thus described by Merriam.' The " Boreal" (Holarctic realm) " Province extends obliquely across the entire continent from New England and Newfoundland to Alaska, conforming in direction to the trend of the northern shores of the continent. It gives off three long arms or chains of islands which reach far south along the three great mountain systems of the United States, a western arm in the Cascades and Sierra Nevada, a central arm in the Rocky Mountains, and an eastern 1 Biological survey of the San Francisco Mountain; N. Amer. Fauna, No. 3, 1890, p. 24. arm in the Alleghanies, and these interdigitate with northward prolongations of the Sonoran" (Medicolumbian) “province, which latter completely surrounds the southern islands of the Boreal" (Holarctic) "system." The faunal relations of the Medicolumbian realm may be tabulated as follows: Baird' divided this region into three districts, which he termed the eastern, central and western. The eastern occupied eastern North America to the central plains, where they exceed 800 feet above sea-level. The western included the territory between the Cascade and Sierra Nevada Mountains and the Pacific Ocean. In my paper of 1875," I adopted the eastern, central and western districts (calling the last the Pacific), and proposed two other districts, viz.: the Austroriparian for the Louisianian division of the eastern of Verrill, and the Sonoran for the southwestern and Mexican Plateau fauna. Merriam, in 1890," proposed a different arrangement. Using the name Sonoran for the entire Medicolumbian Region he divided it into "(1) an Arid or Sonoran subregion proper, occupying the tableland of Mexico, reaching north into western Texas, New Mexico, Arizona, and southern California; (2) a Californian subregion, occupying the greater part of the State of that name; (3) a Lower Californian subregion; (4) a Great Basin region, occupying the area between the Rocky Mountains and the Sierra Nevada, extending as far north as the plains of the Columbia; (5) a Great Plains subregion, occupying the plains east of the Rocky Mountains, and extending north to the plains of the Saskatchewan; and (6) a Louisianian or Austroriparian subregion, occupying the low-lands bordering the Gulf of Mexico and the Mississippi, and extending eastward south of the Alleghanies to the Atlantic seaboard, where it reaches as far north as the mouth of Chesapeake Bay." According to his arrangement the Eastern Region of Baird and myself is not mentioned. This classification may be applicable to birds and mammals; but it is not applicable to the fishes, Batrachia and Reptilia, which are much more exact indicators of the histories of faunæ, owing to their inferior powers of migration. The eastern district or subregion is more nearly allied, from this point of view, to the Austroriparian than the latter is to the Sonoran proper, or arid region. This is due, as Baird previously pointed out, 2 Amer. Jour. Sci. Arts, XCI, 1866, p. 82. |