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 Salmo, 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 



