

The Scottish Naturalist. 



posteriorly, then a- pale belt— bounded by another dark pig- 

 ment-band, but this feature is less marked than in the other 

 form. The head is shorter than in the latter of the same size, 

 and the snout less acute. The shortness of the praeoperculum 

 in the young fish is seldom of great diagnostic value, at least it 

 is not so in our specimens. The maxillary is perhaps somewhat 

 shorter and smaller than in the next group. The vomerine 

 teeth form a double series, but in a zigzag line, differing in this 

 respect both from the young of the common or " yellow" trout, 

 and the young salmon-trout. The number of the pyloric appen- 

 dages, again, in our specimens ranges from 43 to 44. In its 

 migratory condition this fish cannot be mistaken for a common 

 or "yellow" trout; indeed, a well-known angler in the Tay and 

 other rivers in Perthshire at once said it was a salmon-smolt, 

 and held to this opinion. Dr. Young does not appear to have 

 seen this fish, though it is equally a " yellow fin" with the others, 

 and his diagnostic characters — especially those of the vomerine 

 teeth and pyloric caeca — are inapplicable in this case. 



In its fully-developed migratory condition the other " yellow 

 fin " (of the Salmo truita series) has the same dark-bluish or 

 greenish back— as in the salmon-smolt, bright silvery sides, and 

 numerous distinct red spots along as well as above and below 

 the lateral line. There are also many black spots on the sides, 

 and a few on the opercula. The tail has a distinct border of 

 blackish pigment, and then a pale band, bounded by an inner 

 belt of black. The fatty fin, and the dorsal and ventral edges 

 of the caudal are generally bordered with red, the former edge 

 of the tail frequently showing a deeper hue than the latter. 

 The maxillary is comparatively slender. The vomerine teeth 

 form a single series, the points, however, being sometimes 

 inclined alternately right and left. The pyloric caeca in our 

 examples ranged from 49 to 57, the latter number only once, 

 and the next highest being 54. The number given by Dr. 

 Young (59) may be considered above the average ; just as his 

 computation (35) of the pyloric appendages in the common 

 trout is certainly below the mark. 



On contrasting a small "yellow fin" with a salmon-smolt and 

 a common or " yellow" trout of the same size, we find a very 

 interesting gradation in the various characters. The general 

 shape of the salmon-smolt is the most elegant — that of the 



