CHONDROPTERYGII. 585 



LTTGA or ISINGLASS STURGEON, A. huso, of the Caspian Sea, 

 probably the largest species, sometimes weighing, it is said, 

 three thousand pounds, and from which the caviar of commerce 

 is made in great quantities ; the STERLET, A. ruthenus, of the 

 Mediterranean, Black and Caspian seas, which is said to yield 

 caviar of a very superior sort; the LAKE STURGEON, A. rubicun- 

 dus, (Lat. ruddy,) four feet long, of a yellowish red on the 

 back, and olivaceous red on the sides, found in Lakes Ontario 

 and Erie, and the upper lakes ; the Sharp-nosed Sturgeon, A. 

 oxyrhincus, (Gr. sharp-nosed,) seven feet long, and found in the 

 rivers of the United States. A species of the genus Scaphirhyn- 

 cus, (Gr. boat-nosed,) viz: the SHOVEL-FISH, S. platyrhynchus, 

 (Gr. broad-nosed,) is found in the Mississippi river. Of the 

 genus Polyodon, (Gr. many toothed;) is the Spoon-bill, P. 

 folium, (Lat. a leaf,) (previously referred to,) and also an inhabitant 

 of the Mississippi. This fish has an enormous gill-cover, with 

 a large branchial aperture, nearly like that of the generality of 

 fishes; and it is also furnished with an air-bladder: hence, 

 though placed next to the Sharks, Svvainson appears to doubt the 

 propriety of such a position of it. It has a snout greatly ex- 

 tended, much dilated, and, together with the head, nearly as long 

 as the body ; the tail is highly heterocercal, and the skin entirely 

 naked. 



SECOND ORDER. PLAGIOSTOMA. (Gr. Mfiog, plagios, trans- 

 verse ; o-T<ty*a, stoma, mouth.) Gills not free. 



The fishes of this order have a cartilaginous cranium, in which 

 the parts are not separately discernible. The cartilaginous, 

 teeth-bearing jaws are attached to the skull, also by cartilages. 

 The gills are fixed by their external .edges, with five small ex- 

 ternal openings on each side. The face is prolonged in front ; 

 and on its under side is situated the broad transverse mouth ; 

 the ventrals and pectorals, soft and fleshy, like the other fins, are 

 always present ; the pectorals, in the male, having long append- 

 ages on their internal margins. The covering of these fishes 

 consists of shagreen, or of plates variously modified. The 

 swimming-bladder is wanting ; the teeth are placed on the roof 

 of the mouth and the lower jaw. The order includes two fami- 

 lies, Squalida, (Sharks,) and Raiidce, (Rays.) 



(34) SquaKda, (Lat. squalus, a kind of sea-fish.) The SHARKS. 



This dreaded family of fishes are distinguished by having the 

 branchial openings lateral, the eye-lids free, the pectoral fins 

 distinct from the head, the body slender, and somewhat spindle- 



