57 



ORDER VII. CHONDROPTERYGII BRANCHIIS 

 LIBERIS. 



581. We are now arrived at the true Cartilaginous fishes 

 ( 525) ; of which the first order so far resembles the Osseous 

 group, that the gills are connected externally with a single wide 

 opening on each side, furnished with an operculum, or gill-cover. 

 All the Fishes of this order are considered by Cuvier as be- 

 longing to a single family ; but they may be probably better 

 arranged under two families, the ACIPENSERID^, or Sturgeons, 

 and the CHIM^ERID^E, or Chimceras, the former having more 

 affinity to the Osseous fishes, and the latter to the Sharks. The 

 body of the Sturgeon is more or less covered with bony plates, 



arranged in longitudinal rows ; and the head 

 same. The mouth is situated beneath the elongatethmnszle^ and 

 is small and toothless. The air-bladder is very large, and com- 

 municates by a wide opening with the gullet ; and in this, and 

 other points of their internal conformation, the Sturgeons show 

 a considerable approach to the Lizards, whence they are ranked 

 among the Sauroid fishes ( 588). The form of the tail is 

 another mark of resemblance ; for the vertebral column is con- 

 tinued into the upper portion of the caudal fin, the lower one 

 being given off from its underside, instead of stopping short at 

 its commencement, and sending off the upper and lower portions 

 of the fin in the same manner, as in nearly all other Fishes 

 (Fig. 246). Sturgeons, like Salmon, ascend large rivers for the 

 purpose of spawning; and they are the subject of valuable 

 fisheries. They are more abundant in the Continental rivers 

 than in those of Britain ; and are particularly numerous in those 



