The geographical distribution of animals, with a study of the relations ...

;80 DISTRIBUTION OF ANIMALS. [part i.Encyclopaedia Britannica, thinks that as regards that class itcan hardly claim to be more than a sub-region of the Neotropical.These views are mutually destructive, but it will be shown inthe proper place, that on independent grounds the Nearcticregion can very properly be maintained.Subdivisions of the Nearctic Region.—The sub-regions heredepend on the great physical features of the country, and havebeen in some cases accurately definedby American naturalists.First we have the Californiau sub-region, consisting of Californiaand Oregon—a narrow tract between the Sierra Nevadaand the Pacific, but characterized by a number of peculiarspecies and by several genera found nowhere else in the region.The second, or Rocky Mountain sub-region, consists of thisgreat mountain range with its plateaus, and the central plainsand prairies to about 100° west longitude, but including NewMexico and Texas in the South.The third and most important sub-region, which may betermed the Alleghanian, extends eastward to the Atlantic, includingthe Mississippi Valley, the Alleghany Mountains, andthe Eastern United States. This is an old forest district, andcontains most of the characteristic animal types of the region.The fourth, or Canadian sub-region, comprises all the northernpart of the continent from the great lakes to the Arctic oceana land of pine-forests and barren wastes, characterized by Arctictypes and the absence of many of the genera which distinguishthe more southern portions of the region.Observations on the series of Sub-regions.—The twenty-four subregionshere adopted were arrived at by a careful considerationof the distribution of the more important genera, and of thematerials, both zoological and geographical, available for tbeirdetermination ; and it was not till they were almost finallydecided on, that they were found to be equal in number throughoutall the regions—four in each. As this uniformity is of greatadvantage in tabular and diagrammatic presentations of thedistribution of the several families, I decided not to disturbit unless very strong reasons should appear for adopting a greateror less number in any particular case. Such however have not