THE STURGEONS 161 
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 Palzoniscoid; its dermal 
Fig. 165 A. — Chondrosteus acipenseroides. X 3. 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 Palzoniscoids 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. 
