264 THE NATURALIST IX NICARAGUA. [Ch. XIV. 



lusca on the two coasts, separated by the narrow Isthmus 

 of Darien, are almost entirely distinct, whilst we know 

 that since the glacial period there has been little change 

 in the molluscan fauna, nearly, if not all, the shells 

 found in glacial deposits still existing in neighbouring 

 seas. In the Caribbean province, which includes the 

 Gulf of Mexico, the West Indian islands, and the 

 eastern coast of South America as far as Rio de Janeiro, 

 the number of marine shells is estimated by Professor 

 C. B. Adams at not less than 1500 species. From the 

 Panamic province, which, on the western coast of 

 America, extends from the Gulf of California to Payta 

 in Peru, there has been catalogued 1341 distinct 

 species of marine molluscs. Out of this immense 

 number of species, less than fifty occur on both sides of 

 the narrow Isthmus of Darien. So remarkably distinct 

 are the two marine faunas, that most zoologists consider 

 that there has been no communication in the tropics 

 between the two seas since the close of the miocene 

 period, whilst the connection that is supposed to have 

 existed at that remote epoch, and to account for the 

 distribution of corals, whilst advocated by Professor 

 Duncan and other eminent men, is disputed by others 

 equally eminent. No zoologist of note believes that 

 there has been a submergence of the land lying between 

 the Pacific and the Atlantic since the pliocene period, 

 and icebergs would not have floated without such sub- 

 mergence, so that, in the cases I have mentioned, the 

 boulders, if ice -borne, have been carried by glaciers and 

 not by floating ice. 



Whilst I thus found evidences of the ice of the 

 glacial period reaching in the northern hemisphere to 



