THE STURGEONS l ^ l 



genera cannot, therefore, be determined for purpose of 

 comparison. 



The genus of the common sturgeon, Acipenser, is the 

 most completely studied of the recent forms. It includes 

 twenty or more "species," varying in length from one 

 (A. brevirostris, of the Eastern United States) to ten yards 

 (A. huso, of Russia), and is altogether one of the most valu- 

 able food-fishes of the rivers, lakes, and coasts of the north- 

 ern hemisphere. It is a sluggish, bottom-feeding fish, 

 common in muddy streams. Its broad and pointed snout, 

 sensory barbels, and greatly protractile jaws are the most 

 striking differences from the Palaeoniscoid ; its dermal 



Fig. 165 A. Chondrosteus acipenseroides. X \. From Lias of Lyme Regis. 

 (Restoration of skeleton after SMITH WOODWARD.) 



armouring has become reduced to the five longitudinal 

 bands of body plates,* but is more perfect in the tail 

 region ; its skeleton retains an entirely cartilaginous con- 

 dition. In its larval stage conical teeth are known to be 

 present, and the entire series of dermal plates are much 

 larger in relative size. 



A figure of Chondrosteus, a Liassic sturgeon, may here 



* It is interesting to note that in Palaeoniscoids there is sometimes a notice- 

 able tendency for the five rows of plates, dorsal, and the paired lateral and 

 ventral, to increase in size, suggesting the first steps in the origin of the derm 

 plates of Acipenser. 

 M 



