52 Mr. J. S. Miller on Belemnites. 



A longitudinal or transverse fracture of the guard, shows that it is formed 

 of several concentrically "uperposed laminsB perfectly corresponding with 

 those in the chambered cone ; each similarly formed of an arrangement of 

 spathose fibrous crystals forming radii to its curvature, and also covered and 

 cemented together by a very thin nacreous investment, which by being of a 

 less pellucid appearance affords a mark which enables us to trace the thickness 

 of each lamina. 



The circumstance above stated with regard to the division of the belemnitic 

 guard into two or three longitudinal portions, may perhaps authorise the con- 

 jecture, that its laminae were secreted in these separate parts by two or three 

 distinct longitudinal portions or flaps of the animal, laterally touching each 

 other, with irregular edges from whence resulted the irregular suture. 



As the animal, by its situation in the first chamber of the conical multilo- 

 cular shell, cannot form the guard in any other manner than by apposition 

 of its laminae externally, it is rendered thereby certain that this must have 

 been effected by portions of the animal protruding over the edge of the upper 

 chamber, and encompassing the whole of the exterior both of the shell and 

 the guard. 



I have before expressed my opinion, that the laminae of radiating spar 

 interposed between the nacreous layers of the chambered portion, belong to 

 the original organization of the shell, and had not been introduced by subse- 

 quent infiltration ; and I must here repeat the same opinion with regard to 

 the similar laminae of the guard. If we consider the system of nacreous layers 

 alone, abstractedly from the intervening sparry matter, the guard would exhi- 

 bit a texture greatly resembling the bone of the cuttle-fish {Sepia officinalis 

 Linn.) ; namely, a series of concentric calcareous layers, separated by very 

 narrow intervals, and held together by transverse fibres : and such in fact is 

 the appearance it often presents when the sparry matter is removed by partial 

 decomposition. But I cannot persuade myself, that if the spathose substance 

 had been subsequently introduced by infiltration into the cavernous intervals 

 of such a structure, it would have there shot into radiating crystals, without 

 obliterating and destroying all traces of the frail intervening plates. I think 

 that I am able to show that such an obliteration of the internal structure has 

 taken place (with the exception of a few cases) in the instance of echinital 

 and crinoidal remains, which by their conversion into an uniform and peculiar 

 modification of calcareous spar, would afford a case analogous to that of the 

 Belemnite, should we consider the sparry state as superinduced in it. 



I may mention, in support of the opinion here expressed, that the large tu- 

 bular shell found in the Eastern seas, and called by Lamarck Septaria are- 



