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

;190 ZOOLOGICAL GEOGRAPHY. [part in.They are, therefore, at present of comparatively little use forpurposes of geographical distribution, even were it advisableto enter into the subject in a work which will, perhaps, be toomuch overburdened with details only of interest to specialists.Land Shells.—These are very numerous in the warmer partsof the region, but comparatively scarce towards the North.South Europe alone possesses over 600 species, wmereas there areonly 200 in all Northern Europe and Asia. The total numberof species in the whole region is probably about 1,250, of whichthe great majority are Helicidse;the Operculated families beingvery poorly represented. Several small genera or sub-generaare peculiar to the region, as Testacclla (West Europe andCanaries); Leucochroa (Mediterranean district) ;Acicula (Europe);Craspedopoma (Atlantic Islands) ; Lconia (Algeria and Spain)Pamatias (Europe and Canaries) ; Cecina (Mongolia). The largestgenera are Helix and Clausilia, which together comprise morethan half the species ; Pupa, very numerous ; Bidimus andAchatina in moderate numbers, and all the rest smallHelix is the only genus which contains large and handsomespecies ;Bulimus and Achatina, so magnificent in tropical countries,being here represented by small and obscure forms only.Daudehardia is confined to Central and South Europe and NewZealand ; Glandina is chiefly South American ; Hyalina is onlyAmerican and European ; Buliminus ranges over all the worldexcept America ;and the other European genera of Helicidae arewidely distributed. Of the Operculata, Cyclotus, Cyclophorus,and Pupina extend from the Oriental region into Japan andNorth China ;Tudoria is found in Algeria and the West IndiesHydrocena is widely scattered, and occurs in South Europe andJapan. The genera of freshwater shells are all widely distributed.The Pal^earctic Sub-regions.The four sub-regions which are here adopted, have beenfixed upon as those which are, in the present state of our knowledge,at once the most natural and the only practicable ones.