CHONDROPTERYGII. 235 



therefore a suite somewhat parallel to the first, as the Marsupialia, 

 for instance, are parallel to the other unguiculated Mammalia. 



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 projections, depressions, and holes, re- 

 gions analogous to those in the cranium of other fishes may be dis- 

 tinguished. It sometimes happens that movable articulations, 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 ab- 

 sence of the maxillaries and intermaxillaries, or rather in their re- 

 duction 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, vehich in other 

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

 them by a small hole, forms a long cord in several of the Chon- 

 dropterygii, which traverses the bodies of almost all the vertebrae, 

 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, 



Or Chondropterygii, with free hranchm^ 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. 



