FISH AND FISHERIES. 9 
collections, will find themselves so aided by the named species, that instead 
of a difficult study the whole process of learning will be a delightful 
recreation. 
In the wood-cut. at the end of this chapter, fig. 1 represents—A, the 
vomerine teeth; B, the palatine; C, teeth on the tongue; D, supra- 
maxillary ; E, maxillary. These terms will be frequently used. 
Fig. 2. Gill-cover of Salmo salar. A, pre-operculum; B, opercu- 
lum ; C, sub-operculum ; D, inter-operculum. 
Fig. 3. Gill-cover of Salmon trout ; letters the same as above. 
Fig. 4. Salmo salvelinus. 1, pre-operculum; 2, , operculum; 3, 
sub-operculum ; 4, inter-operculum; 5, branchiostegal rays; 6, fixed 
_plates forming immovable posterior margin of the gill-cover ; 7, root of 
pectoral fin. 
These figures are adapted from “Freshwater Fishes of Central 
Europe,” by L. Agassiz, 
Frc, 1.—Mouth of Trout, Salmo fario. 
Fic. 2.—Gill cover of Salmo salar, Salmon. 
Fie. 3.—Ditto of Salmo trutta, Sea-trout. 
Lower Figure—Salmo, head of Salmo. salvelinus of Central Europe. 
B 
