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 smallin size. There are 9 to 11 developed rays 
in the anal fin. The caudal fin is truncate, or va- 
riously concave or forked. There are usually 4o 
to 70 pyloric coeca, 11 or 12 branchiostegals, and 
about 20 (8+ 12) gill-rakers. The sexual pecu- 
liarities are in general less marked than in Ozco- 
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 Sa/ay, 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 
