Vil. (NOMENCLATURE: 
In preparing the generic nomenclature of the Lymnzas, constant 
reference has been made to Dr. W. H. Dall’s recent work on the Land 
and Fresh-Water Mollusks of Alaska, and his conclusions have been 
accepted, in the main, and incorporated in the present work. So far 
as specific nomenclature is concerned, the ruling recognized by Pilsbry 
and other recent zoologists, of “Once a synonym, always a synonym,” 
is the only safe and satisfactory disposition of duplicated names, even 
though the species are here placed in different genera. 
Regarding specific limitations, a wide difference of opinion exists. 
Dr. Pilsbry well says: “The conception of species in such sedentary 
animals as snails is far from simple. A ‘species’ comprises a multitude 
of colonies or communities which at any one time are isolated one from 
the other by the existing topographic and other surface features of 
the country. This is and always has been the case, even with the 
common, widespread forms of the more level part of the country; but 
the colonies there have always been subject to frequent mixture with 
their neighboring colonies, by the ever slightly fluctuating conditions 
of woodland and local moisture, so that their network over the country 
has been here and there made practically complete within comparatively 
short periods. As a consequence, we have in many cases no tangible 
difference between individuals from colonies hundreds of miles apart.” 
The above paragraph, while relating to land mollusks, seems to 
apply equally as well to the Lymnezidz, although the degree of differ- 
entiation is manifestly not as great among the fresh-water pulmonates 
as in the land pulmonates. The same rule, however, holds true for 
both. Land shells are more often differentiated by isolation than are 
the fresh-water pulmonates, but it is true, nevertheless, that isolation 
has played an important part in species formation among the Lymnzas. 
Great care has been used in determining the specific limits of the 
Lymnzas herein recorded. In nearly all cases the types have been 
examined and no name has been placed in the synonomy unless there 
were valid reasons for considering it a synonym. It may be thought 
that too much liberality has been shown in thus recognizing many old 
species long considered synonyms by Binney, Tryon, Dall and other 
competent malacologists, and likewise the addition of such a large 
