THE SALMON FAMILY. 37 
The genus Coregonus, which includes the vari- 
ous species known in America as lake white-fish, 
is distinguishable in general by the small size of 
its mouth, the weakness of its teeth, and the large 
size of its scales. The teeth, especially, are either 
reduced to very slight asperities, or else are alto- 
gether wanting. The species reach a length of 
one to two feet or more. With scarcely an ex- 
ception they inhabit clear lakes, and rarely enter 
streams except to spawn. In far northern regions 
they often descend to the sea; but in the latitude 
of the United States this is rarely possible for 
them, as they are unable to endure impurities in 
the water. They seldom take the hook, and rarely 
feed on other fishes. From their restriction to the 
waters of the different lake systems in which they 
live, numerous local varieties have been developed 
both in Europe and America, distinguished by 
characters less constant and less important than 
those which separate the different species. Euro- 
pean writers have somewhat inconsistently re- 
garded these varying and intangibly different 
forms as distinct species, and many of them have 
come to the conclusion that almost every lake 
system of Scandinavia, Scotland, and Russia has 
several species which are peculiar to it. Dr. Giin- 
ther observes that “the species of this genus are 
not less numerous than those of Sa/mo, some hav- 
ing a very extended geographical range, whilst 
others are confined to very limited localities. 
They are less subject to variation than the trout, 
and therefore more easily characterized and dis- 
tinguished. Hence we find that naturalists who 
