ACIPENSER HUSO. 117 



The cartilaginous jaws are surrounded by a fleshy lip^ which is absent from the 

 middle of the lower jaw. The upper lip is thickest in the middle (Fig. 204). 



The barbels are very near the mouth, and when laid back reach beyond its 

 middle portion ; they are compressed at the base, expanded in the middle, and 

 smooth and pointed at the extremities. 



There are the usual five rows of shields, but they are not strongly developed, 

 so that the body has less of a pentangular aspect than in most of the other 

 species. There are generally twelve or thirteen dorsal shields. Their surfaces 

 are coarsely i-ayed and rough. They are smallest in front ; the sixth to eighth 

 are the largest and highest, while the hindmost have the longest bases, and 

 their spines are directed backward. There are two or four small shields in 

 front of the dorsal fin, arranged in pairs. The lateral shields are forty to forty- 

 five in number. They have a lozenge shape, are very small, but largest in 

 the middle ; they are nearly flat in front, and towards the tail the keel is 

 but little elevated ; their surfaces are pitted, and occasionally show obscure 

 radiation. The lateral line can be traced between them. 



The ten to twelve ventral shields are of median size, thicker than the 

 lateral shields, but less developed than in other species. Their bases are star- 

 shaped in front and round behind ; they are radiated, and have a keel, which 

 extends backward. There are one to three round and rather flat shields. The 

 skin is thickly covered with small spinous bony granules, which form parallel 

 rows. They form irregular groups on the throat, as well as behind the 

 pectoral and ventral fins. On the anterior part of the sides, towards the 

 lateral shields, they become star-shaped. 



The rounded pectoral fin is rather shorter than the height of the body. 

 The bony ray is weak and short. The dorsal fin is twice as long as high, and 

 truncate behind. The upper lobe of the caudal fin is shorter than the head ; 

 the lower lobe is rounded, and is relatively well developed. 



The colour of the snout is yellowish-white. The back is dark ash-grey. 

 The under side of the body and the shields are dirty white. The iris is silvery, 

 with a yellow tinge. 



The differences which appear with age are more remarkable than in other 

 species. As the fishes get older the shields do not increase in size so rapidly as 

 in other species ; and they gradually allow intervals of naked skin to appear 

 between them, and become thinner. The median ridge on the under side of 

 the snout becomes flattened. The bony granules in the skin decrease in size, 

 and in old individuals are only half as large as in young individuals. In a 

 young specimen about a foot and a half long, all the shields of the head are 

 in close contact. Their central points are strongly elevated, and directed 

 backward. The dorsal shields are in contact, and have high, sharp keels and 

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