=The Atlantic Salmon.=—The large species of _Salmo_, called salmon by English-speaking people (_Salmo salar_, _Salmo trutta_), are marine and anadromous, taking the place in the North Atlantic occupied in the North Pacific by the species of _Oncorhynchus_. Two others more or less similar in character occur in Japan and Kamchatka. The others (trout), forming the subgenus _Salar_, are non-migratory, or at least irregularly or imperfectly anadromous. The true or black-spotted trout abound in all streams of northern Europe, northern Asia, and in that part of North America which lies _west_ of the Mississippi Valley. The black-spotted trout are entirely wanting in eastern America—a remarkable fact in geographical distribution, perhaps explained only on the hypothesis of the comparatively recent and Eurasiatic origin of the group, which, we may suppose, has not yet had opportunity to extend its range across the plains, unsuitable for salmon life, which separate the upper Missouri from the Great Lakes. The salmon (_Salmo salar_) is the only black-spotted salmonoid found in American waters tributary to the Atlantic. In Europe, where other species similarly colored occur, the species may be best distinguished by the fact that the teeth on the shaft of the vomer mostly disappear with age. From the only other species positively known, the salmon trout (_Salmo trutta_), which shares this character, the true salmon may be distinguished by the presence of but eleven scales between the adipose fin and the lateral line, while _Salmo trutta_ has about fourteen. The scales are comparatively large in the salmon, there being about one hundred and twenty-five in the lateral line. The caudal fin, which is forked in the young, becomes, as in other species of salmon, more or less truncate with age. The pyloric cœca are fifty to sixty in number.