of ^S^'est India Land Shells. 319 



anotliev. Whether the division (based on the distribution of 

 the Land Sliells) of the West Indies generally into two groups, 

 the one extending eastward from the Northern Continent to 

 Anguilla, and tlie other southerly from AnguiUa to the South 

 American coast, has any connexion with the geological rela- 

 tions of the two mountain chains remarked upon by Humboldt, 

 to which I have already referred, is a curious subject of 

 inquiry. 



The extent to which species vary, especially in the larger 

 islands of the West Indies, deserves notice. Dr. Hooker says, 

 " It has been remarked (Bory de St. Yincent, in Voy. au 

 Quatre lies de V Afriqxie) that the species of islands are more 

 variable than those of continents, an opinion I can scarcely 

 subscribe to, and which is opposed to Darwin's facts, inasmuch 

 as Insular Floras are characterized by peculiar genera, and by 

 having few species in proportion to genera." 



It appears to me that Bory de St. Yincent's observation does, 

 and that "Darwin's facts" do not, apply to land sliells. I admit, 

 however, that even on continents their tendency to variation is 

 considerable. 



Dr. Hooker remarks — "If a genus is numerically increasing, 

 and consequently running into varieties, it will present a group 

 of species with complex relations inter se ; if, on the contrary, 

 it is numerically decreasing, such decrease must lead to the 

 extinction of some varieties, and hence result in the better limi- 

 tation of the remainder." Now, without adopting Dr. Hooker's 

 and Darwin's views as to the origin of species, and their greater 

 limitability by the extinction of varieties, I would state that as 

 in the great majority of the genera of land shells there are 

 numerous groups of species with complex relations inter se, that 

 fact may indicate their comparative recent creation. The geo- 

 logical record,* of prior date to the tertiary formations, has 



* A small fossil body resembling a land shell of the genus Pupa was found by 

 Lyell, with fossil reptilian remains, in the interior of an erect fossil tree in the 

 coal measures of Nova Scotia. 



