392 FISHES. PLECTOGNATHI. 



low, the sides bluish ; fins small, grayish ; lateral plates smaller, 

 and snout and cirri shorter than in the common sturgeon ; skin also 

 smoother. 15 to 25 feet long. Inhabits Caspian and Black Sea. 

 Shaw, v. pi. 159. 



It is from the sounds of this species that the best isinglass is made. 



Gen. 2. SPATULARIA, Shaw. 



Snout very much prolonged, in the form of a spatula ; branchial 

 openings one on each side of the neck, with very large oper- 

 culi ; mouth beneath, with sharp serrated teeth. 



S. reticulata, Shaw. Body subcylindric, tapering to the tail ; head 

 and snout nearly as long as the rest of the body, the snout reti- 

 culated with prominent lines ; lateral line strongly marked ; 

 dorsal fin near the tail ; tail lunated. 12 inches long, young 

 specimens. Shaw, v. pi. 156. 



SUB-CLASS II OSSEOUS FISHES. 



This division includes the fishes with free branchia, and of which the bones, 

 though varying in hardness, are always fibrous. The cranium is divided by sutures. 



ORDER IV. PLECTOGNATHI. 



Bones fibrous ; upper jaw formed by the intermaxillary bone, 

 which is immoveably fixed upon the side of the maxillary ; 

 palatine arch fixed to the cranium ; branchial cleft simple. 



This order approaches the cartilaginous fishes by the imperfection of the jaws and 

 the softness of the bones. The bones, however, are fibrous, and the skeleton has all 

 the structure of the ordinary fishes. The principal distinctive character consists in 

 the maxillary bone being firmly attached to the side of the intermaxillary, which 

 alone forms the jaw ; and the palatine arch, being connected by a suture with the 

 cranium, has in consequence no motion. The operculi and rays are concealed 

 under a thick skin, and nothing is seen externally but a small branchial cleft. Of 

 true ribs but slight vestiges are found, and they are destitute of proper ventral fins ; 

 the intestinal canal is ample, but without ccecums ; and almost all have a swimming- 

 bladder of considerable size. This order comprises two natural families, charac- 

 terized by their teeth. 



FAMILY I. GYMNODONTES. 



This family, in place of apparent teeth, have the jaws furnished with a substance 

 like ivory, divided interiorly into laminae, which are in fact true teeth united. Their 

 operculi are small, with five rays on each side but both imperfectly seen. They feed 

 on Crustacea and fuci. Their flesh is not much esteemed, and that of some spe- 

 cies seems poisonous nt certain seasons. 



Gen. 1. DIODON, Lin. 



Jaws undivided, formed of one piece above and another below, 

 with a rounded portion furrowed across behind the cutting 



