62 SCIENCE SKETCHES. 



teeth. The vomer is flat, its shaft not depressed 

 below the level of the head or chevron (the ante- 

 rior 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 9 to 1 1 developed rays 

 in the anal fin. The caudal fin is truncate, or va- 

 riously concave or forked. There are usually 40 

 to 70 pyloric coeca, II or 12 branch iostegals, and 

 about 20 (8-|-i2) gill-rakers. The sexual pecu- 

 liarities are in general less marked than in Onco- 

 rhynchus ; 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 en- 

 larged, the lower jaw turned upwards at the end, 

 and the upper 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 anadro- 

 mous, taking the place in the North Atlantic occu- 

 pied in the North Pacific by the King Salmon or 

 species of Oncorhynchus. The others (trout), form- 

 ing the sub-genus Salar, are non-migratory, or at 

 least irregularly or imperfectly anadromous. They 

 abound in all streams of northern Europe, north- 

 ern Asia, and in that part of North America which 

 lies west of the Mississippi Valley. The black- 

 spotted trout are entirely wanting in eastern 



