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Delusive appearances are undoubtedly frequently observable, from 
which the presence of the remains of shell may be likely to be in- 
ferred. But these, on close examination, will be found to be entirely 
occasioned by the decomposition and successive exfoliation of the lamina; 
of the spathose substance, of which this body is composed ; and which, 
in many parts, will be found assuming even somewhat of the iridiscent 
appearance of mother-of-pearl. Not finding reason for believing in the 
existence of the shell, or of the supposed contained fluid, I anxiously 
endeavoured to discover in what other state this part of the belemnite 
was most likely to have existed, during the life of the animal. 
Satisfied that the use of the closed chambers, in all the multilocular 
shells, was to bring the animal to which they were appended, with its 
shell, to a degree of specific gravity, so near to that of water, as to render 
it capable of being raised or sunk with facility by the apparatus of its si- 
pliuncle, I concluded that this part of the belemnite must have existed 
in such a state, as by its lightness, it must, like the closed chambers, 
have served as a float to the animal. I had long entertained this opinion, 
before I had made those examinations into the nature of the spines of 
echini, and into the mineral changes of which they were susceptible, by 
which I learned how much the crystallization of the impregnating matter 
would be affected by even a small difference in the nature of the sub- 
stance mineralized. Thus I learned, that a spine of an echinus of one 
species became a mass of opaque, white, rhomboidal crystals; and one of 
another species became a mass of dark brown crystals, of considerable 
transparency, appearing, at the transverse fracture, to radiate from the 
centre, the radii being divided by concentric intersections. 
The general appearance of the crystallization of this latter species of 
spines appearing to be exactly that of the belemnite, it seemed to be 
fair to suppose, that there must have been a close agreement between 
the substance of this species of spine, and that of the belemnites, in their 
original state. 
On examining the recent specimens which accorded with this fossil 
vol. in. s 
