THE FRESH-WATER FISHES OF EUROPE. 



The shields upon the head are more feebly developed than any other species, 

 are only nine in number, and have serrated margins. The first dorsal shield is 

 entirely separated from, and behind the head. The supra-occipital shield is 

 half-moon-shaped, with the convexity directed forward. The epiotic shields 

 are long and narrow, and diverge backward from the sides of the supra-occipital. 

 The parietal shields are small, much smaller than the squamosal, which are pro- 

 longed backward much farther, and extend quite as far forward. The frontal 

 shields extend between the outer border of the squamosal shields and the 



Fig. 203. HEAD OF ACIPENSER HCSO, 

 SEEN FROM ABOVE. 



Fig. 204. HEAD OF ACIPENSER HUSO, 

 SEEN FROM BELOW. 



nares, passing just above the eyes, and converging a little forward. They do 

 not meet in the median line, or touch the parietal shields; and the middle line 

 of the skull is occupied by a furrow (Fig. 203). 



The eyes are small, round, of equal size, and placed vertically over the 

 mouth. They look outward and upward, are far from the outline of the head 

 when seen from above, and are separated by eight times the orbital diameter. 

 The narines are small and nearly equal in size. The outer sides of the snout 

 are covered with pores, and similar pores are seen on its under side divided by 

 a short broad median ridge. The mouth is far in advance of the middle of the 

 length of the under side of the head, and occupies nearly its entire breadth. 



