of West India Land Shells. 337 



crease in iieiglit, being in Porto Rico nnder 4,000, in the Virgin 

 Islands less than 2,000, and in Virgin Gorda only a few hnn- 

 dred feet. The strait which lies between Virgin Gorda and 

 Angnilla separates the region just referred to from the islands 

 to the south, in some of which there is still active volcanic 

 agency. In this latter chain of islands, the mountains rise 

 from 2,500 to 5000 feet. Anguilla, at the northern extremity, 

 and Barbuda and Barbadoes to the eastward of the chain, have 

 comparatively but little elevation. 



The number of species of land shells described by Pfeiffer in 

 his Monographs and publications of later date, exceeds 6000, 

 of which nearly one-sixth inhabit the "West Indies.* This 

 appears, perhaps, the less extraordinary, when it is considered 

 that about one-half of all the known species are peculiar to 

 islands. 



Darwin, in his " Origin of Spocies," remarks : — " The species 

 of all kinds which inhabit oceanic islands are few in number, 

 compared with those on equal continental areas. Alph. de 

 Candolle admits this for plants, and WoUaston for insects." 

 The author adds, " Although in oceanic islands the number of 

 kinds of inhabitants is scanty, the proportion of endemic species 

 {i. e. those found nowhere else in the world) is often extremely 

 large." Dr. J". D. Hooker, in his " Introductory Essay to the 

 Flora of Tasmania," observes, that the total number of spe- 

 cies which islands contain, seems to be invariably less than an 

 equal continental area possesses ; and the relative numbers of 

 species to genera (or other higher groups) are also much less 

 than in similar continental areas." , 



Xow it is true with respect to land shells, that the proportion 

 of insular endemic species is great, but the number of species, 

 and also their number relatively to genera, far exceed in amount 

 those which inhabit equal continental areas. By way of illus- 



* In using the general term " West Indies," I include Bermuda, and also 

 Curasao, and the adjacent island of Buen Ayre. 



