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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 laminae 

 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 siphuncle, 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 substance 

 mineralized. Thus I learned, that a spine of an echinus of one species 

 became a mass of opaque, white, rhomboidal crystals ; and one of an- 

 other 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. III. S 



