F^REFACE. 



The following memoir by Mr. William H. Dall, of the U. S. Geological Survey, is a 

 ■continuation of the subject of the Tertiary MoUusca of Florida, by the same author, which 

 was published in Vol. 3, Part I. of these Transactions. This memoir completes the 

 different groups except the Pelecypoda. 



In addition to the collections available in the preparation of Part L, much new 

 material has since been studied, which was obtained in later explorations by various 

 members and correspondents of the U. S. Geological Survey ; by Mr. Charles W. John.son, 

 -Curator of the Museum of this Institution, and by the writer. 



To the enumeration and description of the species actually collected, Mr. Dall has 

 added many notes on other related fossils from the Eocene and other horizons, when it 

 seemed desirable. 



This course has been pursued witli the intention of making the work more useful to 

 students of our Tertiary fossils. 



In some cases this has extended to a review of an entire group, as known from our 

 Tertiary beds ; and it is hoped that this scrutiny may result in an important advance in the 

 revision of our Tertiary MoUusca — a work which will require the efforts of students for a 

 long time to bring to a satisfactory completion. 



To Major J. W. Powell, Director of the U. S. Geological Survey ; to various members 

 of the Survey and obliging correspondents, and to the authorities of the Smithsonian 

 Institution and the U. S. National Museum our thanks are due for assistance rendered in 

 the prosecution of the present investigation. 



We are also indebted to the U. S. Geological Survey for authority to reproduce and 

 use the geological map of Florida which appears in this volume, and which was recently 

 issued as one of the illustrations to Bulletin 84 of the U. S. Geological Survey, in which 

 •the present state of our knowledge of the geology of that State is fully discussed. 



JOSEPH WILLCOX. 

 Philadelphia, December 12, 1S92. 



