LYMNZIDZ OF NORTH AMERICA. XI 
Chapter X includes the bibliography, which is comparatively ex- 
haustive, although a few references have doubtless been overlooked. 
It is believed to contain all of the important references to the subject. 
Of the 211 names occurring in the literature, 95 are herein ad- 
mitted as worthy of recognition as species or races. 6 names are 
used for the first time. 35 fossil species have been recorded, of 
which 24 are here recognized. One new race is described. The 
absence of keys for the determination of the species may lead some 
readers to suppose that the author places no value on aids of this 
character. Such is not the case, and many attempts have been made to 
prepare a satisfactory key to aid beginners, but without success. In a 
group like the Lymnzas, where variation is paralleled in so many of 
the species, it is obviously impossible to prepare a key which will be 
intelligible to any save those well versed in the subject, and for this 
class no key is necessary. It is believed that with the figures and de- 
scriptions no one will have serious difficulty in determining the ma- 
jority of the species of American Lymnezas. 
It is fully realized, in presenting this monograph, that there is 
much contained therein which is faulty and incomplete. In a few 
cases adequate material has not been available for a satisfactory treat- 
ment of the species. There are many records which have not been 
substantiated and have been omitted, therefore, from the records and 
distribution maps. In a number of cases the soft parts have been lack- 
‘ng and a definite placing of the species has been impossible. With all 
its shortcomings, however, the author believes that it is a step in ad- 
vance of previous efforts, and that it will prove an aid to all students 
of this interesting family. | 
Should this volume meet with the approval of the conchological 
public, it is in the mind of the author to prepare companion volumes 
or Planorbis, Physa and related genera. 
FRANK COLLINS BAKER. 
Chicago, Illinois, January, 1911. 
