OF NORTH AMERICA. 119 



A large number of valuable papers have been published which de- 

 scribe and illustrate various species of Lymngeas 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 Lymnseas 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. 



