64 Mr. J. S. Miller on Belemnites. 



from such a decay, an accidental cavity, which may be distinguished from the 

 cavity of the chambered part by its difference in form ; the accidental cavity 

 being of the form of a more elongated cone, and having also frequently a pro- 

 jecting point arising from matter accidentally indurated in the central canal, 

 above noticed, as having been mistaken for the continuation of the siphuncle. 



In some fragments of Belemnites, two conical cavities have been observed ; 

 one of these is undoubtedly the cavity of the chambered shell, the other has 

 arisen from the accidental falling out of a portion of the guard. 



On immersing the guard in dilute acid, we discover that animal matter in- 

 tervenes in small quantity between the fibrous crystals. 



If, as I have supposed, the guard was originally of a crystalline structure, it 

 would certainly present great obstacles to decomposition. This is indeed 

 proved by the shells of the genus Pinna ; the only ones, I believe, which, 

 having a texture resembling that of the Belemnites, are found both in a recent 

 and a fossil state. The fossil Pinnae found in the lower beds of the London 

 clay at Bognor, and in the Paris beds, retain distinctly the same structure as 

 the recent ones. 



The fibrous shell so frequent in the oolite (supposed to be an oyster and 

 described as Ostrea Trichites, but evidently from its peculiar organization 

 belonging to a distinct genus) and the Inoceramus of the chalk, presents a 

 fibrous and more or less crystalline texture, which in these cases no one has 

 ever doubted to have belonged to them in their original state. 



I have seen, in the collection of Richard Bright, Esq., many specimens 

 where Belemnites had been imbedded in flint, and have been dissolved out; and 

 in the hollows which they had occupied, are remaining siliceous casts of those 

 spherical bodies with connecting fibres which the Rev. W. D. Conybeare has 

 described in the 3rd volume of the Geological Transactions as resulting from 

 the infiltration of silex into cavities formed by some boring animal. Mr, Allan 

 has also figured these bodies in Belemnites in the Edinburgh Transactions. 

 In Mr. Bright's specimens, some small portions of the radiating calcareous 

 spar of the guard of the Belemnite are remaining among the connecting 

 siliceous threads. 



Von Tressau observes, as a proof of the indestructibility of the Belemnites, 

 that those found in iron mines along with Ammonites and Nautili, have sustain- 

 ed no change, whilst the latter are converted into ochre. 



The Belemnite in fact rarely occurs otherwise than with such a texture as 

 may present on fracture a fibrous spathose organization ; and where this has 

 been penetrated by silex or other mineral substances, it has always, and but 

 with only one exception, destroyed its peculiar formation. 



