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 Eussia, 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, Arion, Limax, Buliminus, 

 and Clausilia. 



(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 Mac^daria, Iberus, Fomatia, and Xerophilct) and Buli- 

 minus {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 headquarters 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 Neritina, 

 occur in southern Spain and Austria, Galicia, and southern 

 Eussia, 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 Eussia and the Caucasus. 



The Palaearctic region falls into three sub-regions : — 



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



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



