go Salmonidz 
rhynchus. 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 sal- 
monoid 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 cceca are fifty to sixty in number. 
The color in adults, according to Dr. Day, is “superiorly of 
a steel-blue, becoming lighter on the sides and beneath. Mostly 
a few rounded or X-shaped spots scattered above the lateral 
line and upper half of the head, being more numerous in the 
female than in the male. Dorsal, caudal, and pectoral fins 
dusky; ventrals and anal white, the former grayish internally. 
Prior to entering fresh waters these fish are of a brilliant steel- 
blue along the back, which becomes changed to a muddy tinge 
when they enter rivers. After these fish have passed into the 
fresh waters for the purpose of breeding, numerous orange 
streaks appear in the cheeks of the male, and also spots or 
even marks of the same, and likewise of a red color, on the body, 
