48 Mr. J. S. Miller on Belemnites. 



the great difficulty was, how so small an apparatus should move so heavy a 

 spathose body as the protecting shell or guard. To overcome this_, each of the 

 authors created a theory, agreeing in the conclusion, that the guard was ori- 

 ginally light and porous, and has obtained its present solidity by the process 

 of petrifaction, 



Walch conceives that the guard of the Belemnite was formed of two hollow 

 shells, inclosing a viscous fluid ; the chambered cone being inserted into this 

 cavity, its siphuncle passing through the fluid and terminating at the point 

 of the shell. On this view the fluid in question would have produced specific 

 lightness, and might as he conceives have been converted into radiating spar, 

 and thus furnished the present appearance. 



Mr. Parkinson supposed that the guard as well as the chambered apparatus 

 was intended to increase the animal buoyancy. Hence, from a resemblance 

 of the guard to some supposed echinital spines in the chalk, he refers to the 

 internal organization of echinital spines ; and finding this to be porous or cork- 

 like, he conceives the guard to have been originally of a similar consistency, 

 but now altered by the infiltration of calcareous spar. He further thinks, with 

 reference to the tube observed by Walch as existing in the Belemnitic guard, 

 that it might have been a continuation of the siphuncle ; and this, communicating 

 with the cellular substance of the guard, might by the admission of air or water 

 have served to regulate the buoyancy thus acquired. 



Lamarck conceives that the Belemnite was an internal shell once inclosed 

 within the body of the animal, similar to the bone of the Sepia, and conse- 

 quently like that bone, of a spongy or cellular form, 



n. Generic character. 



Genus. Belemnites. A cephalopodous ? molluscous animal provided with a 

 fibrous spathose conical shell, divided by transverse concave septa into se- 

 parate cells or chambers connected by a siphuncle ; and inserted into 

 a laminar, solid, fibrous, spathose, subconical or fusiform body extending 

 beyond it, and forming a protecting guard or sheath. 



HI. Observations. 



I have already observed that the Belemnites are now admitted to have inha- 

 bited the sea; but as we are not acquainted with any living animals possessed 

 of a similar structure, we must necessarily form our ideas respecting the ani- 

 mal of the Belemnite from the hints which its shell is capable of furnishing, by 

 the muscular impressions it exhibits, and by its analogy to other testacea. 



The conical chambered shell is easily separated by decomposition from its 

 protecting guard, which being of a solid laminar spathose substance is very 



