GEOGRAPHICAL DISTRIBUTION. 11$ 



tute what are called Varieties of the species. The conditions 

 of environment existing at a specific centre, or metropolis of 

 the species, as Forbes called it, constitute the normal habitat 

 for that species. The particular morphological and structural 

 characters which the species express are called its typical 

 specific characters. The modifications from these typical 

 characters which are seen in representatives of the species 

 on the borders of its specific distribution are its varietal 

 characters. 



The Distinctness of the Flora and Fauna of Distinct Provinces. 

 The species associated together in a natural-history prov- 

 ince are the flora and fauna of that province, and as generally 

 defined, not over one half of the species of two distinct prov- 

 inces are identical; or, to put it in the converse form, about 

 half the species of any province are distinct, or peculiar to 

 that province. Such a rule is purely arbitrary, and will vary 

 greatly as applied by different naturalists, but such a general 

 rule is applied in the distinguishment of the provinces of 

 marine species. 



The Various Classifications of Natural-history Provinces. In 

 the classification of provinces in Woodward's "Manual of 

 Mollusca" we find eighteen such marine provinces recognized, 

 and the land regions are defined under twenty-seven names. 

 Sclater (1857) defined six terrestrial regions, which were after- 

 wards adopted by Wallace (1876) * and subdivided into twenty- 

 four sub-regions. Fischer (1887) combined and extended the 

 former classification, and defined thirty regions distributed in 

 the following seven zones, viz. : Palearctic, African paleo- 

 tropical, Eastern paleotropical, Australian, Neantarctic, Neo- 

 tropical, Nearctic. Each of these regions is again subdivided 

 into sub-regions with their special faunas ; as, for example, the 

 region Circamediterranean is the second of the Palearctic 

 regions ; this is subdivided into the sub-regions (a) occidental 

 or Atlantic, (b) Meridional or Mediterranean (with the four 

 Faunas, Hispano-Barbaresque, Egypto-Syrienne, Hellado- 

 Anatolique, and Italo-Dalmate). (c) Centrale or Pontique, 

 (*/) Orientale or Caspique.f 



* A. R. Wallace, " The Geographical Distribution of Animals," 1876. 

 f Paul Fischer, "Manual de Conchyliologie," Paris, 1887. 



