﻿REPORT ON LAND AND FRESH WATKK SHELLS 



COLLECTED IX THE BAHAMAS IX [904, HY 



MR. OWEN BRYANT AND OTHERS. 3 



Bi WILLIAM HEALEY DALL 



The Bahama islands are particularly interesting to American 

 naturalists, as affording the development of tropical fauna nearest 

 to us; but especially as containing the most valuable evidences of 

 evolution in living animals within a geologically short period ot 

 time. There is no doubt that the entire archipelago has been below 

 the surface of the sea not earlier than the end of the Pliocene, and 

 that the present land and fresh water fauna has developed from 

 ancestors which have reached the islands since that time, from 

 adjacent lands. Among the various kinds of airbreathing animals 

 none are more suitable for a study of evolutionary processes in a 

 very uniform and of late very stable environment, than the Pul- 

 monate gastropods. Slow to migrate ; profuse in reproduction ; 

 affected by a relatively small number of environmental factors ; pre- 

 serving their variable characters chiefly in their shells, which are 

 easily collected and require the assistance of no taxidermist to pre- 

 serve from decay ; lending themselves readily to fossilization, easily 

 observed and maintained in a living state — they form ideal objects 

 for the study of the questions involved. 



Only recently has the effect of isolation on islands shut in by 

 marine barriers been appreciated in its relations to developmental 

 problems, and of all localities accessible to us, where these problems 

 can be studied with ease and without exposure to pestilential condi- 

 tions none compares with the vast group of rocks and islands known 

 as the Bahamas. 



So far, little advantage has been taken of these opportunities, and 

 the work which has been done by Henry Bryant, J. J. Brown. Gov- 

 ernor Rawson, Weinland, the U. S. Fish Commission, the expedition 



1 Mr. Bryant desires me to state that this report is the fifth of a series 

 based on collections made by G. M. Allen, T. Barber, and Owen Bryant 

 during part of the summer of 1904. In the present case a representative 

 series of Mr. Bryant's shells is contained in the collection of the National 

 Museum, as a donation from the collector. The Bahama localities in the 

 text are taken from Mr. Bryant's labels, except where otherwise indicated. 



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