136 SALMONID^. 



forms fully one half of the border of the free gill-cover, and is 

 finely grooved. The gill rays are twelve in number. 



The dental system of the Mackinaw Salmon is very complete, 

 and more formidable than in any other member of the family. 

 The intermaxillaries and labials, as well as the palatine bones, 

 lower jaws, and tougue, are armed with very sharp and strong 

 conical curved teeth ; those on the vomer consisting of a circu- 

 lar cluster on the knot of that bone, and of a double roAv extend- 

 ing at least half an inch backward. 



The dorsal fin is situated in the middle of the fish, and con- 

 tains fourteen rays, the eighth ray being exactly central between 

 the snout and the tip of the central caudal fin-ray. The second, 

 adipose, dorsal fin, is small and obtusely formed. The caudal 

 fin has nineteen^ the ventrals, each nine, the anal eleven, and 

 the pectorals, each fourteen rays. The origin of the central fins 

 is slightly posterior to the centre of the fish. 



Such are the principal structural distinctions of this noble fish, 

 and I have entered into these rather at length, since by them 

 only can he be distinguished from his lake congeners. I have 

 already observed the great differences existing in point of colour 

 and mai'kings between fish of the same species found in dif- 

 ferent waters, throughout this family, and endeavoured to show 

 the impropriety of founding specific distinctions, or even per- 

 manent varieties, by reference to these alone, without reference 

 to structure. In the Salmo Fontinalis, common Brook Trout, 

 this is easy to be noticed, but in none of the Salnionidce with 

 which I am acquainted, are the differences of colour and marking 

 so broad and distinct, as in different individuals of this species. 

 I have before me^ as I write, three coloured representations of 



