74 



FISH GALLERY. 



Paddle- 

 fish. 



Sword- 

 bill. 



The Chondrosteidse (e. g. 200), which may be regarded as a 

 connecting link between the ancient Palseoniscidse and the modern 

 Sturgeons, include Chondrosteus, from the Lower Lias of England, 

 and Gyrosteus, from the Upper Lias of Yorkshire. There are no 

 scutes in the skin, but the dorsal lobe of the tail-fin is armed with 

 fulcra and clothed with rhombic scales. The mouth is small, 

 situated on the under side of the snout, and without teeth in the 

 adult. The eye is set far forward ; there are numerous branchio- 

 stegal rays. 



In the Polyodontidae, a modern family including the Paddle- 

 fish of the Mississippi valley (211), and the Sword-bill Sturgeon of 

 the rivers of China (212), the scales in the skin are very small and 

 isolated ; the tail is heterocercal, and is armed with fulcra on the 

 upper edge, the snout is much prolonged, and without barbels. 

 The mouth is large, with minute teeth ; the bones of the cranial 

 roof form a discontinuous shield; there are no spines to the 

 pectoral fins. 



The Paddle-fish or Spoon-bill Sturgeon, Polyodon folium, 211, 

 is sluggish in its habits and feeds chiefly on the minute organisms 

 contained in the mud which it consumes. The gill-rakers are 

 long and fine, and form an efficient filter, preventing the food 

 particles escaping through the gill-slits with the expiratory current 

 of water. The paddle-shaped rostrum of the fish is used for 

 stirring up the mud, and serves also as an organ of touch, necessary 

 to the animal in consequence of the smallness of the eyes and the 

 muddiness of the water which renders distinct vision impossible. 

 The Paddle-fish reaches an occasional length of six feet and a 

 weight of 120 lbs., but the average size is from 10 to 30 lbs. The 

 Sword-bill Sturgeon, Psephurus gladius, 212, has a tapering 

 rostrum,, and the fulcra of the fins are fewer and of larger size 

 than those of the Paddle-fish. The Sword-bill is said to attain a 

 length of 20 feet ; in its habits and mode of life it resembles the 

 Paddle-fish. 



In the Acipenseridse, or Sturgeons proper, there are five longi- 

 tudinal rows of keeled plates or scutes, and also small, irregular, 

 stellate scutes scattered throughout the skin ; the mouth is small, 

 inferior, suctorial, and without teeth in the adult, and there are 

 four barbels in front of the mouth. There are fulcra on the front 



