198 AMERICAN JOURNAL 



then all the varieties which inhabit a locality should have been 

 affected. In that case, all the varieties in any given place 

 would have the same geographical limits. But the contrary 

 more frequently occurs. Each variety has its own limits of 

 distribution. If a few coincide in the boundary of their pro- 

 vince, on the other hand one is often found to have an extent 

 of distribution, which is equal to that of two or more other 

 varieties. But such a geographical coincidence of one variety 

 with several other varieties is inconsistent with any other 

 theory than that of an original constitutional peculiarity of 

 character in each variety. This inference is confirmed by the 

 occasional intermingling in one locality of varieties, which 

 differ from each other as much as those which occupy distinct 

 regions. If, then, we assume the original independent creation 

 of all the varieties, each originally represented by at least sev- 

 eral individuals, the facts of distribution become explicable 

 with the greatest facility. 



" The same statements might be made respecting entire spe- 

 cies, and even groups of species and genera. Some are very 

 local, and others, more widely distributed, occupy the ground 

 of several local species." 



The very local distribution of the terrestrial Mollusca in the 

 West Indies* did not escape the attention of Professor Adams. 

 In "Hints on the Geographical Distribution of Animals, with 

 especial Eeference to the Mollusca," ("Contrib.," pp. 207 — 215, 

 Oct., 1852,) a paper which contains many original and sugges- 

 tive remarks, he mentions that the terrestrial faunae of Cuba, 

 St. Domingo, Porto Rico and Jamaica, are distinct from each 

 other; and that the same is true, to a great extent, of the West 

 India Islands generally; that those of the Bahamas and Ber- 

 mudas are also distinct. Jamaica, he says, "contains more 

 known species of land Molluscs than the whole of North 

 America, from the Isthmus to Melville Island." 



Referring to the relations of the subject discussed in the 

 paper in question, to theories of the origin of species and to 

 geological reasoning, Professor Adams makes the following 

 among other observations: — 



"If large groups of such islands as the West Indies should 

 be united in a common area of dry land, then, according to 

 the theory which accounts for the facts of distribution by ac- 

 tual dispersion from centres, there would be zoological pro- 

 vinces containing five to tenfold as many species as any which 

 now exist. 



"The geological fact, that continents by submergence be- 



* See paper " On the Geographical Distribution of the Genera and Spe- 

 cies of Land Shells of the West India Islands, with a Catalogue of the 

 Species of each Island." By T. Bland, Ann. N. Y. Lyceum, vii., 1861. 



