FAMILY OP STURGEONS. 291 



grow more or less during the whole period of their 

 lives, and many of them, accordingly, are by far the 

 largest of the true fishes, attaining, in many cases, 

 even to enormous dimensions. 



In these fishes the gills are either free, as in the 

 generality of fishes, or they are fixed by having tho 

 outer edge attached to the skin, so that the water 

 can find admission to the spaces between them only 

 by holes in their surface. This peculiarity affords 

 the means of making two divisions, both of which 

 have representatives in Britain. To the first of 

 these. Cartilaginous Fishes with free Gills, 

 belongs 



XXVI. FAMILY OF THE STURGEONS. 

 STURIONIDiE. 



Representatives in British Fauna. Gen. 1. Sp. 2. 



Gen. 103. Acipenser. Sp. 214. ^. sturio. Common Stm-geon. 

 215. A. lateralis. Broad- nosed ditto. 



This family is composed of a single genus, con- 

 taining the well known and highly valuable Stur- 

 geons. They are at once known by the elongated 

 and angular body, defended by longitudinal rows of 

 large indurated plates of a pyramidal form with the 

 apex pointed. The snout is depressed and conical ; 

 the mouth tubular and without teeth, and placed 

 on the underside of the head, at some distance be- 

 hind the extremity of the snout. Our indigenous 



