The Scottish Naturalist. 231 



trout least so ; the distance between the fatty fin and the origin 

 of the caudal rays, moreover, is shortest in the common trout, 

 and longest in the salmon. The dark back of the "yellow 

 fin," its silvery sides and cheeks, and the silvery and whitish 

 belly, stand in strong contrast with the young river-trout. 

 The red spots on the sides are much more developed in the 

 latter than in the " yellow fin ; " while in the smolt they are 

 only faintly seen after rubbing oft" the scales. 



The pectorals of the " yellow fin " are dull or brownish 

 orange, often closely resembling those of the common trout in 

 colour, though they sometimes possess a little more blackish 

 pigment. In the salmon-smolt they are occasionally darker 

 with a tinge of green (Stormontfield specimen). There is like- 

 wise a regular gradation as to the shape of the fin, which is 

 largest in the trout and most pointed in -the salmon; the 

 " yellow-fin " holding an intermediate position. 



The dorsal of the " yellow fin " presents a few red spots 

 amongst the dark, as in the common trout, and there is the 

 same gradation in regard to size, being largest in the trout, 

 least in the smolt. In a "yellow" trout and a " yellow fin" of 

 the same length there is a very appreciable difference in the 

 position of this fin, which is decidedly further forward in the 

 latter, — the same variation occurring in the fatty, ventral, and 

 anal, as noticed in the first glance at the fish. Dr. Giinther 

 observes that " the interneural spine of the first long dorsal 

 ray is attached to the seventeenth vertebra," and in the "yellow 

 fin" this is found to be the average, the first ray in the "yellow'' 

 trout being a few vertebra? further back. 



The reddish edge of the fatty fin is most marked in the 

 common trout, is present in a less degree in the " yellow fin ! ' 

 (though in some scarcely noticeable), and is absent in the 

 smolt. The blackish pigment at the base of this organ is more 

 developed in the " yellow fin " than in the trout. It is need- 

 less to add that no scientific naturalist would base his 

 distinctions of such species on colours alone, far less on the 

 colour of a fin. 



The tail of the " yellow fin " is more deeply cleft than in the 

 common trout, and the rays longer, — the smolt, however, sur- 

 passing it in both characters. The border of blackish pigment 

 is more evident in the " yellow fia : ' than in the trout. The 



