﻿Vlli INTRODUCTION 



I have endeavored to give fairly full descriptions of all the 

 shell characters where they are of any importance and to de- 

 scribe the different features of the female shells of dimorphic 

 species. Comparisons have been made between closely related 

 species or those which resemble each other. 



In a few cases changes have been made, as it has been pos- 

 sible to examine gravid material since the writing of the Sy- 

 nopsis, which proved that the position assigned to these forms 

 was erroneous. 



The subject is brought down to January i, 1913. But I 

 have included references to the new genera described by Dr. 

 Haas in January', which had been illustrated prior to that 

 time in the new edition of the Conchylien Cabinet. 



Charles Torrey Simpson. 



Little River, Florida, 

 February i, 1913. 



