The Sea-Trout. 283 



such spots, but the vast majority of the species 

 have none at all. The bull-trout itself is marked 

 out from all the allied species by the greater thick- 

 ness of its neck, the more angular form of its gill- 

 covers, the somewhat smaller size of its scales, and, 

 in the full-grown fish, the more convex formation 

 of the tail-fin. 1 Distinctions between it and its 

 friends will also be found both in the shape and in 

 the relative position of the other fins ; but as these 

 vary more or less in different stages of growth, they 

 afford a less certain test of the species. The teeth, 

 however, offer a ready means of distinguishing the 

 sea-trout at least in the earlier period of its exist- 

 ence from the bull-trout and the salmon. All the 

 three species have only a single series of vomerine 

 teeth, or teeth on the central bone in the roof of 

 the mouth (and in this lies the difference between 

 them and the common river -trout, which has a 

 double row), but they are most numerous in the 

 sea-trout; and though these teeth are gradually 

 lost in all the migratory species as the fish ap- 

 proaches mature age, in the sea-trout they are 

 always retained for a longer period than in either 

 the bull-trout or the salmon. 2 If, after an ex- 



1 Pennell's Angler Naturalist, p. 244 et seq. 



2 Many points in the history of the Salmonoids still remain 

 very obscure. Dr Giinther, in his ' Study of Fishes,' says : " We 

 know of no group of fishes which offers so many difficulties to the 



