xviii BRITISH FRESHWATER FISHES 



The mouth may be terminal or inferior, small or 

 large, toothed or toothless, according to the manner 

 of life. Above the mouth two pairs of bones are 

 articulated with the anterior part of the skull, the 

 praemaxillaries in front and the maxillaries behind ; 

 the praemaxillaries usually meet in the middle line, 

 but in the Pike they are widely separated, and in the 

 Eels they are absent ; the maxillary is often provided 



Head of Schelly (Coregonus stigmaticus]. 

 Op. operculum ; sop. suboperculum ; top. interoperculum ; 

 pop. prse-operculum ; br. branchiostegal rays ; so. 

 suborbitals ; pro. prse-orbital ; n. nostrils ; pmx. 

 pnemaxillary ; mx. maxillary ; smx. supramaxillary ; 

 inn. lower jaw. 



with one, and in the Shad with two supramaxillary 

 bones attached to its upper edge. In the more 

 generalized types (Salmon, Shad, Pike, etc.) the prae- 

 maxillaries are non-protractile and are much shorter 

 than the maxillaries, which enter the gape and may 

 be toothed, but in many fishes the praemaxillaries 

 nearly or quite exclude the toothless maxillaries from 

 the border of the mouth, and the latter merely act as 

 a lever for the protrusion of the former. The mouth 



