LYMNIDZ OF NORTH AMERICA. 119 
A large number of valuable papers have been published which de- 
scribe and illustrate various species of Lymnzas but the ones men- 
tioned above are the most extensive and the nearest approach to a 
monographic treatment. Of these, the monograph by Binney is the 
most complete. 
In much of the previous work on this group of mollusks it is ap- 
parent that little attention has been given to a critical examination of 
type material, without which it is impossible to accurately determine 
the relations of the different species. Many of the figures and de- 
scriptions are poor and quite unrecognizable without an examination 
of type or authentic material. In the preparation of the present mono- 
graph, nearly all of the types of American Lymnzas have been ex- 
amined and it is believed that, in most cases, the species have been 
satisfactorily elucidated. The illustrations are photographs of authen- 
tic specimens. 
