CHONDROPTETIYGIT. 225 



The skeleton of the Chondropterygii is essentially cartilaginous ; that is, it 

 Contains no osseous fibres, the calcareous matter being deposited in small 

 grains, and not in filaments ; hence the absence of sutures in their cranium, 

 which is always formed of a single piece, but in which, by means of projec- 

 tions, depressions, and holes, regions analogous to those in the cranium of 

 other fishes may be distinguished. It sometimes happens that moveable arti- 

 culations, which are found in other orders, are not met with in this one; part 

 of the vertebrae of certain Rays, for instance, being united in a single body. 

 Some of the articulations of the bones of the face also disappear, and the most 

 apparent character of this division consists in the absence of the maxillaries 

 and intermaxillaries, or rather in their reduction to mere vestiges concealed 

 under the skin, while their functions are fulfilled by bones analogous to the 

 palatines, and even sometimes by the vomer. The gelatinous substance, which 

 in other fishes fills the intervals of the vertebrae, and only communicates with 

 them by a small hole, forms a long chord in several of the Chondropterygii, 

 which traverses the bodies of almost all the vertebra?, without scarcely varying 

 in diameter. 



This series is divided into two orders the Chondropterygii whose branchiae 

 are free, like those of ordinary fishes ; and those in which they are fixed, that 

 is to say, attached to the skin by their external edge in such a manner that 

 the water can only escape from their intervals through holes on the surface. 



ORDER I. 



STURIONES, OR CHONDROPTERYGII BRANCHIIS 

 LIBERIS, 



OB Chondropterygii with free branchits, which are still closely allied to the 

 ordinary fishes in their gills, which have but a single wide opening, and are 

 furnished with an operculum, but without rays in the membrane. This 

 order comprises but two genera. 



ACIPENSER, LinncBUS*. 



The general form of the Sturgeon is similar to that of the Shark, but the 

 body is more or less covered with bony plates in longi- 

 tudinal rows ; the exterior portion of the head is also 

 well mailed; the mouth, placed under the snout, is 

 small and edentated; the palatine, soldered to the 

 maxillaries, converts them into the upper jaw, and 

 vestiges of the intermaxillaries are found in the thickness of the h'ps. This 

 mouth, placed on a pedicle that has three articulations, is more protractile 

 than that of a Shark. The eyes and nostrils are on the side of the head, and 



* Acipensir is the ancient name ; Sturio, whence Sturgeon, is modern, and is probably 

 the German name Stoer latinized. 



