Fragments of fossil trout, very imperfectly known, are recorded chiefly from Pleistocene deposits of Idaho, under the name of _Rhabdofario lacustris_. We have also received from Dr. John C. Merriam, from ferruginous sands of the same region, several fragments of jaws of salmon, in the hook-nosed condition, with enlarged teeth, showing that the present salmon-runs have been in operation for many thousands of years. Most other fragments hitherto referred to _Salmonidæ_ belong to some other kind of fish. =Coregonus, the Whitefish.=—The genus _Coregonus_, which includes the various species known in America as lake whitefish, 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 slight asperities, or else are altogether wanting. The species reach a length of one to three feet. With scarcely an exception 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 never possible for them, as they are unable to endure warm or impure water. They seldom take the hook, and rarely feed on other fishes. Numerous local varieties characterize the lakes of Scandinavia, Scotland, and Arctic Asia and America. Largest and most desirable of all these as a food-fish is the common whitefish of the Great Lakes (_Coregonus clupeiformis_), with its allies or variants in the Mackenzie and Yukon. The species of _Coregonus_ differ from each other in the form and size of the mouth, in the form of the body, and in the development of the gill-rakers. _Coregonus oxyrhynchus_—the _Schnäbel_ of Holland, Germany, and Scandinavia—has the mouth very small, the sharp snout projecting far beyond it. No species similar to this is found in America. The Rocky Mountain whitefish (_Coregonus williamsoni_) has also a small mouth and projecting snout, but the latter is blunter and much shorter than in _C. oxyrhynchus_. This is a small species abounding everywhere in the clear lakes and streams of the Rocky Mountains and the Sierra Nevada, from Colorado to Vancouver Island. It is a handsome fish and excellent as food. [Illustration: FIG. 49.—Rocky Mountain Whitefish, _Coregonus williamsoni_ Girard. ] Closely allied to _Coregonus williamsoni_ is the pilot-fish, shad-waiter, roundfish, or Menomonee whitefish (_Coregonus quadrilateralis_). This species is found in the Great Lakes, the Adirondack region, the lakes of New Hampshire, and thence northwestward to the Yukon, abounding in cold deep waters, its range apparently nowhere coinciding with that of _Coregonus williamsoni_. [Illustration: FIG. 50.—Whitefish, _Coregonus clupeiformis_ Mitchill. Ecorse, Mich. ]