ACKNOWLEDGMENTS 



IN LARGE ^MEASURE the successful preparation of this work has 

 been due to the help and encouragement of many American concholo- 

 gists and zoologists. The authorities of the United States National 

 Museum at Washington, through the interest of Dr. Paul Bartsch, Curator 

 of Recent and Cenozoic Invertebrates, have freely lent the collections of 

 Planorbidae for study. Without this magnificent material, probably the 

 largest assemblage of species of this family extant, it would have been 

 imjiossible to understand the relationships of the American species of the 

 family. ]Mr. William J. Clench, Curator of the Department of Mollusca, 

 ]\Iuseum of Comparative Zoology of Harvard University, supplemented the 

 National Museum material by the loan of thousands of specimens, many 

 of the series of species being incomparable in size and completeness. Both 

 of these gentlemen have also contributed much anatomical material. Other 

 individuals and institutions have lent or given specimens for both anatomi- 

 cal and dry study. To all of these the writer is under the greatest obliga- 

 tion. The list of those rendering assistance is given below: 



Dr. C. C. Adams, Director, State Museum of New York, Albany 



Dr. E. A. Andrews, Professor of Zoology (Retired), Johns Hopkins University, 



Baltimore 

 Dr. H. BuRRiNGTON Baker, Professor of Zoology, University of Pennsylvania, 



Philadelphia 

 Dr. John C. Bequaert, Professor, Harvard University Medical School, Cambridge 

 Dr. Edward W. Berry, Professor of Paleontology, Johns Hopkins University, 



Baltimore 

 Dr. S. Stillman Berry, Redlands, California 

 Dr. Stanley T. Brooks, Curator of Lower Livertebrates, Carnegie ]\Liseum, 



Pittsburgh 

 Dr. A. R. Cahn, formerly Associate Professor of Zoology, University of lUinois, 



Urbana 

 Dr. E. P. Cheatum, Professor of Zoology, Southern IMethodist Universit}', Dallas 

 Dr. William A. Clemens, formerly of the Pacific Biological Station, Nanaimo, B.C. 



Now Professor of Zoology, University of British Columbia, Vancouver, B.C. 

 Miss Ruth E. Coats, Tellamoole, Oregon 

 Dr. Ernest C. Faust, School of Tropical ^ledicine, Tulane University, New 



Orleans 

 Mr. C. J. Firkins, Edwardsville, Illinois 

 Dr. Thural Dale Foster,* University of Illinois, Urbana 

 Mr. Calvin Goodrich, Curator of ]\Ioilusca, University of Michigan Museum, Ann 



Arbor 

 Dr. G. D. Hanna, Curator of Paleontology, California Academy of Science, San 



Francisco 

 Professor Junius Henderson,* Curator Emeritus, University Museum, Univer- 

 sity of Colorado, Boulder 

 Dr. L. G. Hertlein, Assistant Curator of Paleontology, California Academy of 



Science, San Francisco 

 Mr. Shintoro Hirase,* Zoological Institute, Tok3-o, Japan 



Dr. William A. Hoffman,* School of Troi)ical Medicine, San Juan, Puerto Rico 

 Mr. Leslie Hubricht, St. Louis Botanical Gardens, St. Louis, Missouri 

 Mr. A. Jankowski, Warsaw, Poland 



Mr. A. LaRocque, Canadian Geological Survey, Ottawa, Canada 

 Mr. John B. Litsey, Dallas, Texas 



*Deceased. 



xi 



