522 



GEOGEAPHICAL ZOOLOGY. 



[part IV. 



Family 30.— HELICINIDiE. (7 Genera, 433 Species.) (1868.) 



General Distribution. 



The Helicinidse are very characteristic of the Antilles, com- 

 paratively few being found in any other part of the world 

 except the Islands of the Pacific. The genera are : — 



Trochatdla (33 sp.), Antilles with a species in Venezuela, and 

 another in Cambodja ; Lucidella (5 sp.), Antilles ; Helicina {214, 

 sp.), Antilles, Pacific Islands, Tropical America, Southern 

 United States, Moluccas, Australia, Philippines, Java, Andaman 

 Islands and North China ; Schasicheila (5 sp.), Mexico, Guate- 

 mala and Bahamas ; Alcadia (28 sp.), Antilles ; Georissa (5 sp.) 

 Moulmein to Burraah. About 10 per cent, of new species 

 appear to have been since described in the larger genera of this 

 family. 



General Observations on the Distribution of the Land Mollusca. 



A consideration of the distribution of the families and genera 

 of land-shells shows us, that although they possess some special 

 features, yet they agree in many respects with the higher animals 

 in their limitation by great natural barriers, such as oceans, 

 deserts, mountain ranges, and climatal zones. A remarkable 

 point in the distribution of these animals, is the number of 

 genera which have a very limited range, and also the prevalence 

 of genera having species scattered, as it were at random, all 

 over the earth. No less than 14 genera (or about one-sixth of 

 the whole number) are confined to the Antilles, while the 

 greater part of the sub-genera of modern authors are restricted to 

 limited areas. 



If we first compare the New "World with the Old, we find the 

 difference as regards genera quite as great as in most of the 



