194 THE BERMUDA ISLANDS. 



a few forms both of gasteropods and pelecypods common to 

 the Mediterranean and Gulf Provinces), but also, through the 

 agency of floating materials, trees, etc., swept from rivers, 

 land mollusks may have been transported across the Atlantic, 

 just as they have been carried by the Gulf Stream from the 

 West Indies to the outlying island of Bermuda, 1 a distance of 

 over 700 miles. 



A further development of the same idea explains certain 

 peculiarties in the distribution of species common to the 

 Pacific and the Gulf of Mexico. The presence of Miocene and 

 Pliocene deposits render it certain that there was communica- 

 tion between the Gulf and the Pacific across the Isthmus of 

 Panama as late as the Pliocene. And a portion of the equa- 

 torial current probably swept directly through to the Pacific. 

 Thus it is likely that those forms common to both sides of the 

 isthmus, will prove to be of Atlantic origin, and to have been 

 distributed westward. 



The indigenous Bermudian mollusk-fauna, marine as well as 

 terrrestrial, has undoubtedly been derived wholly 2 from the 

 West Indies. And since the island is typically oceanic, "a 

 solitary peak rising abruptly from a base only 120 miles in 

 diameter," surrounded on all sides by between 2500 and 3000 

 fathoms depth, we have an idication here that land mollusks 

 of many families, Helicidse, Zonitidse, Succinidae, Pupidte, Heli- 

 cinidae, even Vaginulidse (for a large undescribed species of 

 Vaginidus exists upon the island), may be transported far out 

 to sea, and, in all probability, by the agencies mentioned above. 



The considerable divergence existing between the various 

 species of the zonitoid genus peculiar to Bermuda, Poecil- 

 ozonites, indicates that the island is of considerable antiquity. 



We may define the genus as follows : 



1 See Darwin, Origin of Species, 6th ed., p. 353. Also a paper by Mr. C. T. 

 Simpson, On the Distribution of Land and Fresh-water Shells in the Tropics, Conch. 

 Ex. ii, p. 37, 50. 



2 See on this point the chapter on the " Relationship of the Bermudian Fauna," 

 ant., p. 88. A. H. 



