64 THE OLD RED SANDSTONE. 
variably agreeing, and the wanting portions invariably agree- 
ing als) ——it seems but natural to conclude that an original 
difference must have obtained, and that the existing parts, 
which we can at once recognize as bone, must have been 
united to parts now wanting, which were composed of car- 
tillage. The naturalist never doubts that the shark’s teeth, 
which he finds detached on the shore, or buried in some an- 
cient formation, were united originally to cartilaginous jaws. 
Now, in breaking open all the ichthyolites of the Lower Old 
Red Sandstone, with the exception of those of the two fami- 
lies already described, we find that some of the parts are in- 
variably wanting, however excellent the state of preservation 
maintained by the rest. I have seen every scale preserved 
and in its place—one set of both the larger and smaller 
pones occupying their original position— jaws thickly set 
with teeth still undetached from the head —the massy bones 
of the skull still unseparated —the larger shoulder-bone, on 
which the operculum rests, lying in its proper bed — the oper- 
culum itself entire — and all the external rays which sup- 
port the fins, though frequently fine as hairs, spreading out 
distinct as the fibres in the wing of the dragon-fly, or the 
woody nerves in an oak-leaf. In no case, however, have I 
succeeded in finding a single joint of the vertebral column, 
or the trace of a single internal ray. No part of the internal 
skeleton survives, nor does its disappearance seem to have had 
any connection with the greater mass of putrescent matter 
which must have surrounded it, seeing that the external rays 
of the fins show quite as entire when turned over upon the 
body, as sometimes occurs, as when spread out from it in 
profile. Besides, in the ichthyolites of the chalk, no parts 
of the skeleton are better preserved than the internal parts — 
the vertebral joints, aad the internal rays. The reader must 
