'381 



CHAPTER XT. 



rUESII-WATER FISHES OF THE ORDEll GANOIDET. 



FAMILY ACIPENSEKID.E— Genis Acipensek : Acipenser glabor— Sterlet— A. gmelini— A. 

 stellatus — A. scliypa — A. guldenstudtii — A. naccarii — A. nardoi — A. heckelii — A. nasus — 

 The Sturgeon— A. huso. 



Family: ACIPENSERID^. 



Genus: Acipenser (ApxTeiji). 



The Sturg-eons are a small group of fishes^ forming- a distinct division of 

 the class. The body is elong-ated, and almost cylindrical, tapering- conically to 

 the tail. They have the tail fashioned on the heterocercal plan, in which the 

 rays are chiefly developed on the lower lobe of the caudal fin, and the vertebral 

 column is prolong-ed into the upper lobe. The skeleton is cartilag-inous. The 

 skin is commonly armoured with bony bucklers, which, in this genus do not 

 unite into a continuous armour, but occur in five long-itudinal rows, leaving- the 

 skin between them exposed, or defended only with small scattered bony scales. 



The head has the snout produced far in front of the mouth, which is 

 situate on the under side. Between the mouth and the extremity of the snout 

 are four barbels in a transverse series. 



The cartilaginous framework of the head is covered with armour. The 

 shields are more or less quadrate. The elong-ated snout is formed by a prolon- 

 g'ation of the vomerine element below, and the nasal and ethmoid elements 

 above. The nostrils are double, and in front of the eye. The mouth is pro- 

 tractile, toothless, transverse, relatively small, and lies in a cartilag-inous pro- 

 tuberance, formed of three elements. 



Its anterior edg-e is marg-ined by thick lips, which are often rudimentary at 

 the angle of the mouth. 



The eyes are placed laterally, behind the nares, and commonly differ in size 

 on the two sides of the head. The gill-cover appears to correspond partly to the 

 operculum of bony fishes, and partly to the sub-orbital arch. The gills are 

 arranged like those of bony fishes. The gill membranes at the throat are con- 

 fluent, and united to the isthmus between them. There are no branchiostegal 

 rays. The true gills are four in number, comb-like, with their points free, and 

 there are two accessory gills. On the upper edge of the operculum there is a 

 small spiracle. 



