50 SALHONIDiE. 



orbit of the eye; while in that of the Bull Trout {Salmo Eriox), 

 it will run obliquely very far below it. 



This distinction is very easy of observation^ and is extremely 

 important in the definition of species ; as indeed is everything 

 connected with the form and peculiarities of the head, not 

 forgetting its relative proportion to the entire length of the 

 body. 



Of no less value is the arrangement of the teeth in the 

 different classes, families, and species of fish ; there being, on 

 this point, infinitely greater variety than can be imagined by 

 persons who have given their attention only to the structure of 

 quadrupeds. 



" The teeth," says Mr. Yarrel, in the introduction of his 

 fine work on British Fishes — from which I have taken the 

 liberty of borrowing the last cut, descriptive of the gill -covers 

 and dental system of the Salmon, Bull Trout, and Common 

 Trout — " of fishes are so constant, as well as permanent in 

 their characters, as to be worthy of particular attention. In 

 the opinion of the best icthyologists, they are second only to the 

 fins, which in their number, situation, size and form, are 

 admitted to be of first-rate importance, 



" Some fishes have teeth attached to all the bones that assist 

 in forming the cavity of the mouth and pharynx, to the inter- 

 maxillary, the maxillary, and palatine bones, the vomer, the 

 tongue, the branchial arches supporting the gills, and the 

 pharyngeal bones. Sometimes the teeth are uniform in shape 

 on the various bones, at others differing. One or more of 

 these bones are sometimes without teeth of any sort; and 

 there are fishes that have no teeth whatever on any of 



