STXJEGEONS. 
151 
endued 'witli considerable powers of feeling and taste; in wbicb 
sensations they are aided by the barbs which hang from the 
under surface of the snout. The fifth, or infraorbital pair of 
nerves, which are particularly the organs by which sensation 
or feeling is distributed, is furnished to the snout and barbs; 
while the facial branch of the nerve of hearing proceeds to 
the integuments of the mouth and lips, and also to the gill- 
covers, thus offering no slight support to the opinion that 
Sturgeons are susceptible of the influence of sounds, as well 
as of other acute sensations. 
In the nostrils also these fishes differ from the Sharks and 
Skates, by having them placed above the snout, and in front 
of the eyes, where it is usual to find them in the fishes 
characterized by the usual bony skeleton. The form of the 
body, and especially of the tail, approaches to that of the 
Sharks; but the resemblance of the latter becomes less on 
close inspection; for although the lobes are unequal, and the 
vertebral column is continued along the upper lobe to the end, 
the fin itself is distinctly supported by branched rays, as in 
many of the fishes belonging to other tribes. The general 
texture of the skin bears a near resemblance to what is found 
in Skates, being soft, and thickly covered with mucous pores; 
but the bony plates on the sides and head possess a texture 
and use which differ from what is generally found in plagi- 
ostomous fishes, and cause this fanarly to display a closer 
approach to a class which Mons. Agassiz has denominated the 
Placoid race; of which a large proportion is only found fossil, 
but of which one of the distinguishing characters is that they 
have on their bodies a defence of plates, shields, or scales, 
which are covered with a thick and firm coat of enamel. 
These plates are arranged in lines lengthwise on the body, 
and on the head and cheeks are flattened into shields; closely 
pressed together, in something like regular order, but without 
that strict orderly arrangement, at least along the middle line 
of the head and snout, which has been claimed for them, and 
by which it has been supposed some separate species might be 
defined. 
Professor Owen supposes that the intention of this special 
armature on the head and body is chiefly for protection in 
the situations which these fishes frequent. They were designed, 
he says, to be the scavengers of the great rivers; they swim 
