X THE PALAEARCTIC REGION 285 



probably proceeds along the snowy mountains west of Setchouan, 

 the Pe-ling and Tan-sia-shan ranges, so as to include all the 

 high ground of Thibet and of the upper waters of the Hoang-ho, 

 and ultimately reaches its eastern limit at some point on the 

 shores of the Sea of Japan. 



The region thus includes all Europe, Africa north of the 

 Sahara, with the Atlantic islands (the Azores, Canaries, etc.). 

 North Arabia, Asiatic Turkey, the greater part of Persia, 

 Afghanistan, Thibet, all Asiatic Russia, and a very large portion 

 of the Chinese empire. 



The principal characteristics of the region as a whole are : — 



(1) The rich development of Helix, Avion, Limax, Buliminus^ 

 and Qlausilia. 



(2) The comparative absence of land operculates (see map, 

 frontispiece). 



(3) The uniform character of the fresh-water fauna. 



It is in the southern portion of the region that Helix (in the 

 sub-genera Macularia, Iberus, Pomatia, and Xerophild) and 

 Buliminus (^Zehrina, Chondrula, Una) attain their maximum. 

 In the north, Fruticicola is the characteristic group ; in the 

 mountainous districts of the south-east, Campylaea, with 

 Clausilia. The Arionidae have their head-quarters in the 

 damp and warm regions of western Europe, but are rare in 

 the south. They only approach the Mediterranean coast in 

 Algeria, near Gibraltar, and in the region between the base of 

 the Pyrenees and the Maritime Alps, and are very poor in 

 species throughout Italy and Sardinia. They are absent from 

 almost the whole of northern Africa, the Mediterranean islands 

 (except Sardinia), the whole Balkan district, the Crimea, 

 Caucasus, and western Asia.^ 



The uniformity of the fresh-water fauna is disturbed only 

 in the extreme south. A few species of Melanopsis, with Weri- 

 Una, occur in southern Spain and Austria, Galicia, and southern 

 Russia, while a Melania or two (absent from Spain) penetrate 

 the south-eastern parts of Europe as far as Germany. Cyrena 

 begins to replace Cyclas in southern Russia and the Caucasus. 



The Palaearctic region falls into three sub-regions : — 



(1) The Northern or Septentrional Sub-region, i.e. the dis- 



1 Pollonera, Boll. Mus. Zool. Torino, v. 1890, No. 87. 



