FOREWORD 



Sixty years have passed without a comprehensive re- 

 vision and monograph of this Important and Interesting family. 

 The writer has been, for a number of years, engaged In collect- 

 ing and consolidating data In connection with the group and has 

 also had access to and acquired long series of the few common 

 species and a considerable number of the rarities. 



The present work is based largely upon this material, 

 although in many cases it has been necessary to draw solely 

 upon original descriptions of the respective authors, and also 

 reproduce certain of their none too satisfactory illustrations. 



A further study of the soft parts will, no doubt, result 

 in changes in the position of certain genera. 



The author wishes to acknowledge his gratitude to Dr. 

 James Hartley Beal, Dr. Henry A. Pllsbry, Dr. Edward M. Davis, 

 Dr. Paul Bartsch, Dr. Harold Rehder, Mrs. Jeanne Schwengel, 

 Dick Albany, and others, for their kindness and many favors in 

 connection with this work. 



