X The Molluscan Family Planorbidae 



The anatomical drawings in this work have all been made by the author 

 with the aid of the camera lucida, and the outlines and much of the detail 

 of the figures are correct from the standpoint of dimensions. Some of 

 the finer details have been filled in by hand on the camera lucida figure. 

 All dissections were made with a Spencer binocular microscope with mag- 

 nification up to seventy-five diameters. The radulae have all been examined 

 under a Zeiss microscope with magnification up to about 1000 diameters. 



In order that the features of the different organs might be fully known 

 they have been separated and otherwise dissected to bring out all rela- 

 tionships. In many cases sections have been made through organs or 

 groups of organs the better to show structural conditions. Some of the 

 figures are diagrammatic, but in the majority of the figures the author has 

 endeavored to portray the form of the organs as they appeared to him 

 under the microscope. Only the shells of the type species of the different 

 genera and subgenera are figured in the plates prepared for Part I. 



In the matter of bibliographic citations it has not been deemed neces- 

 sary to include all references to works in which a genus or other group is 

 listed or described. To have done this would have lengthened the work 

 to a large degree without adding greatly to its value. Only the most im- 

 portant citations, including the first one in which the generic name ap- 

 pears, are included. It will be noted that many groups, which have been 

 ignored or placed in the synonymy by previous authors, have been recog- 

 nized in this work. This is particularly true of Asiatic groups which have 

 been little known anatomically. Every generic or group name has been 

 given careful study to ascertain its true relationship. 



All groups described in this work are arranged under the heading of a 

 genus or of a subgenus, none as sections. Until a greater number of species 

 have been examined for the internal organization this division appears 

 best. Some of the groups herein considered genera may later be placed as 

 subgenera. It does not at present appear to be of any advantage to recog- 

 nize the terms section or subsection for any of the groupings. 



The list of species included in each genus or subgenus has no pretension 

 to completeness, only those species being listed which have either been 

 examined anatomically or appear from the form of the shell to be related. 

 As additional material is examined some of the species listed may be 

 shifted to other groups and additional species may be included. 



January, 1942 



