Vol. XT Allen, Origin and Distribution of N. A. Birds. II9 



1893 J 



species so we may have in zoogeography subregions, sub- 

 Lovinces, and even snbfauncc. In addition to and independent 

 of these divisions we may also recognize zones. To illustrate by 

 an example, temperate North America forms a region of a 

 realm and includes two subregions, one of which is divisible 

 into provinces and subprovinces, and some of these latter into 

 districts, while each may contain several fauna. It also proves 

 desirable to subdivide the continent into a number of transconti- 

 nental belts or zones, which in a way coincide with the climatic 

 zones of the physiographer. 



The term fauna is unfortunately in current use both in a 

 o-eneral sense and also in a restricted, taxonomic sense. In the 

 first case it is employed to designate the animal life of a given 

 area ^eooraphical or political, varying in extent from a town- 

 ship'to a continent, from a transient pool to a lake or an ocean, 

 or in creoW from a definite stratigraphic horizon to a geologic 

 ao-e as the" qualifying words may chance to indicate; in the 

 second case it is a definite taxonomic term for the ultimate sub- 

 divisions of a realm, as is the term species for the ultimate 

 divisions of a class. The term flora has also the same double 

 use • and it would perhaps be futile to attempt to displace either 

 bv 'some specially coined substitute, to take the place of these 

 terms when used in a specific sense for an ultimate faunal 

 or floral area. Such an attempt, however, is perhaps unnecessary, 

 since the qualifying prefix will rarely, if ever, leave one in doubt 

 as to whether the tennis used in a general or in a taxonomic 



sense. 



Realms are sometimes characterized by the presence of certain 

 orders, and usually by the presence of certain families which give 

 to them a particular impress, and by the absence of others which in 

 a similar way characterize other realms. Regions are usually 

 characterized by the prevalence over them of certain genera, or 

 even by entire families ; provinces by the prevalence of particular 

 eenera or by the presence or absence of prominent species. 

 Fauna, on the other hand, are seldom characterized by having 

 restricted to them any particular genera or species, but by the 

 combination or overlapping of a number of genera and species 

 not found elsewhere associated-in other words, by a peculiar 

 commingling of a considerable number of genera and species. 



