158 LOWER VERTEBRATES. 



The fact that the humijbaclc salmon runs only on' alternate years in Puget Sound 

 (1875, 1877, 1879, etc.) is well attested and at present unexplained. Stray individu- 

 als only are taken in other years. This species has a distinct ' run,' in the United 

 States, only in Puget Sound, although individuals (called ' lost salmon ') are occasion- 

 ally taken in the Columbia and in the Sacramento. 



Numerous attempts have been made to introduce the quinnat salmon into the 

 waters of the eastern states and of Europe. Individuals thus planted have been 

 taken in several different localities, but, as yet, not in any considerable number. 



The genus Salmo comprises those forms of salmon and trout which have been 

 best and longest known. As in related genera, the mouth is large, and the jaws, 

 palatines, and tongue are armed with strong teeth. The vomer is flat, its shaft not 

 depressed below the level of the head or chevron (the anterior end). There are a few 

 teeth on the chevron ; and behind it, on the shaft, there is either a double series of 

 teeth or an irregular single series. These teeth, in the true salmon, disappear with 

 age, but in the others (the black-spotted trout), they are persistent. The scales are 

 silvery, and moderate or small in size. There are nine to eleven develoj^ed rays in 

 the anal fin. The caudal fin is truncate, or variously concave or forked. There are 

 usually 40 to 70 pyloric coeoa; 11 or 12 branchiostegals, and about 20 (8 -|- 12) gill 

 rakers. The sexual peculiarities are in general less marked than in Oncorhynchus; 

 they are also greater in the anadromous species than in those which inhabit fresh 

 waters. In general, the male in the breeding season is redder, its jaws are prolonged, 

 the front teeth enlarged, the lower jaw turned ujDwards at the end, and the upjjer jaw 

 notched, or sometimes even perforated, by the tip of the lower. All the species of 

 Salmo (like those of Oncorhynchus) are more or less spotted with black. 



Two species (salmon) are- marine and anadromous, taking the place, in the North 

 Atlantic, occupied in the North Pacific by the species of Oncorhynchus. The others 

 (trout), forming the sub-genus Solar, are non-migratory, or, at least, irregularly or 

 imperfectly anadromous. They abound in all streams of northern EuroiDC, northern 

 Asia, and 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 explainable only on the hypothesis of the compara^ 

 tively recent and Eurasiatic origin of the group, which we may suppose has not yet 

 had time to extend its range across the plains, unsuitable for salmonoid 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 Eurojic, where other species similarly colored 

 occur, the species may be best distinguished by the fact that the teeth on the shaft of 

 its vomer mostly disappear with age. From the only other sjjecies jjositively known 

 {Salmo trutta) which shares this character, the true salmon may be known by the 

 ]presence of but about eleven scales between the adipose fin and the lateral line, 

 while Salmo trutta has about fourteen. The scales are comjDaratively large in the 

 salmon, there being about 125 in the lateral line. The caudal fin, which is foi-ked in 

 the young, becomes, as in other species of salmon, more or less truncate with age. 

 The pyloric ccBca are fifty to sixty in number. 



The following account of the coloration of the salmon is from Dr. Day's fishes of 

 Great Britain : — " Color in adults superiorly of a steel blue, becoming lighter on the 

 sides and beneath. Mostly a few rounded or x-shaped spots scattered above the lal^ 

 eral line and upper half of the head, being more numerous in the female than in the 



