58 Mr. J. S. Miller on Belemnites. 



which^ a new spathose and nacreous lamina was secreted over the guard ; an 

 effect not capable of being produced, had the guard originally possessed a la- 

 minar cavernous organization. 



I believe it will be proved by further researches, that all chambered shells 

 are inclosed in, or capable of being covered and encompassed by, the animal ; 

 for without such a contrivance, that nice degree of buoyancy which they are 

 intended to furnish to the animal would be destroyed by the adhesion of 

 parasitic testacea, from which a perfect protection is thus obtained. From 

 the size of the animal and the smallness of the outer chamber, it is clear that 

 the inhabitant of the Belemnite could never entirely withdraw within the shell; 

 and it appears probable that the guard, independent of its use in preserving 

 a well-adjusted buoyancy, was also intended to furnish to the muscles an 

 abutment and support on which they could adhere, and from which, like a 

 fulcrum, they could receive additional strength. 



The surface of the two lateral muscles which encompassed or clasped the 

 guard, had each a distinct power of secretion, although they formed their 

 laminae at the same time. This accounts for the sutures which separate the 

 guard into two longitudinal portions. These muscles, in some specimens 

 appear not to have increased in proportion to the laminae they encompassed, 

 and therefore, when the guard greatly enlarged, to have been unable to secrete 

 other laminae completely surrounding the former. Hence arises sometimes 

 a groove on one side, frequently in old specimens displaying the shortening 

 of the laminae as they accumulated and as the edges of the muscles were with- 

 drawn. 



In some species the muscles appear to fold together near the apex, and form 

 two or three grooves in this part ; while in others they lap over the apex and 

 form a mamillar termination. In very perfect specimens we may observe 

 in some species a longitudinal slit in the guard where it adheres to the cham- 

 bered cone, evidently also arising from the causes cited before. On the guard 

 of such specimens we may distinctly trace impressions of the branching blood- 

 vessels in each of the two longitudinal muscles ; which furnishes, in my opi- 

 nion, a most satis/actor?/ evidence that the guard was really enveloped by them 

 in the manner in which I have stated. 



Description of the Species. 



In endeavouring to fix specific characters to the various Belemnites that have 

 fallen under my observation, and which I have considered as distinct species, I 

 ought to state that they are chiefly derived from that part which I have called 



