PREFACE. 
The fresh-water snails embraced in the family Lymneide form 
an important factor in the mollusk fauna of the more northern coun- 
tries of the world. Say, Haldeman, Lea, Tryon, Binney and other early 
writers have described many species and several of these authors have 
essayed more or less complete monographs of the family. In 1865, 
W. G. Binney monographed the Lymnzas in the series of illustrated 
papers published in the Smithsonian Miscellaneous Collections under 
the litle of ‘“Land and Fresh-Water Shells of North America.” Bin- 
ney was naturally very conservative and reduced the then known spec- 
ies and varieties (79) to about one-third this number (31). Though 
expressing his opinion that certain species were synonymous with 
certain other species, he was careful to include descriptions and figures 
of all known forms, leaving the matter to the judgment of American 
conchologists to weigh and test his conclusions. Unfortunately the 
American conchologists did not do this, but accepted Binney’s con- 
clusions as final, thus greatly complicating the literature and rendering 
the use of the latter for geographic purposes almost impossible. 
The present monograph was begun as a revision of Binney’s work ; 
but, as the matter progressed, it became evident that the old classifi- 
cations and methods of presentation needed an almost complete revo- 
Intion to meet the requirements of modern standards. The meager 
descriptions needed to be much more extensive, the exact geographic 
and geologic distribution needed to be indicated, the ecology as well as 
other items demanded attention, and the project has thus grown to 
many times its original dimensions. It was also evident that to ade- 
cuately present the subject a large number of figures would be neces- 
sary and these have accordingly been made from authentic or type 
material. It is obvious that until a group in any branch of Zoology is 
placed upon a sound basis and the limits of the species accurately de- 
fined, no discussions of zodgeographic questions can be of any value. 
This fact has been clearly demonstrated in the course of the present 
work. 
It is the purpose of this volume to furnish to students of this 
family of fresh-water mollusks a reliable guide to a knowledge of 
the species, of their habitat relations and their geographic range. To 
this end chapters more or less extensive, have been introduced briefly 
