of ^Vest India Land Shells. 341 



terrestrial mollusks, but do not believe in any save very trifling 

 modifications of species being induced by local conditions and 

 influences. Causes now in operation are insufiicient to account 

 for tlie present distribution of land shells on such groups of 

 islands as the "West Indies, and speaking generally, I can only 

 refer the origin of their faunas to creation subsequent to the 

 elevation of the insulated areas. 



Such insular faunas, Professor Adams remarks, "prove that 

 the islands which they inhabit, have been geographically sepa- 

 rate since an era anterior to the introduction of the existing 

 species." But this conclusion, he adds, " does not depend on 

 the assumption that the species would have dispersed them- 

 selves over several islands, if they had not always been re- 

 strained by water ; but on the fact that such small zoological 

 provinces exist nowhere on continents." 



Pfeiffer, in his Monographs, divides the inoperculate land 

 shells, including the Proserpinacese, into thirty-three genera, 

 of which twenty are specitically represented on the continents 

 of America, and eighteen in the West India Islands. The sub- 

 joined table shows the distribution of the latter. Ceres, peculiar 

 to North America (Mexico), and Anostoma, Tomigerus, and 

 Megaspira, belonging to the southern continent, are not found 

 in the islands, and Ennea and Proserpina are wanting on the 

 continents. 



It will be seen that Yitrina of North America, and also Pro- 

 serpina, belonging to that part of the continent by afiinity, are 

 found only in the islands west of Portorico, while of the genera 

 of the southern continent Streptaxis is represented only in 

 Trinidad, Clausilia in Portorico, Tornatellina in Portorico and 

 islands east and south* of it, and Balea in Cuba. As regards 

 genera, and also the relative number of species, as shown in 



* Here, and in the tables, I refer to those islands of which lists of species are 

 given in the catalogue. With the islands actually east and south of Portorico I 

 include Curajao and Buen Ayre. 



