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food, but travels only upon the guard or rampart, leaving a trail behind, 

 as all land-snails do; which, hardening into a testaceous substance, 

 increases the dimensions of the outer walls, both in length and thick- 

 ness, from the cell or chamber, to the bottom, or point of the whole 

 belemnite. The animal, in its progress and return, clasps the whole 

 guard, as a snail does a small branch of a tree in the gardens ; and 

 where the two sides meet, there the sulcus is formed." 



An objection offers itself to this opinion of Mr. Platt, which is, that 

 the conical concamerated part is sometimes much wider than the spa- 

 those part of the belemnite : a circumstance which by no means agrees 

 with Mr. Platt's conjecture. According to his opinion, the upper cham- 

 ber should agree, in its circumference, with the upper, or widest part of 

 the belemnite ; the body of the belemnite acquiring a proportional 

 accession of bulk on the formation of each superadded chamber. But, 

 as may be seen, Plate VIII. Fig. 8, specimens exist, in which the cir- 

 cumference of the later formed chambers exceed, in their circumference, 

 that of the widest part of the body of the belemnite : an incongruity 

 which militates much against Mr. Platt's opinion, as to the formation 

 and increase of this body. 



Having now placed before you the opinions of these respectable natu- 

 ralists, we will proceed at once to the examination of this fossil, and of 

 the several parts which enter into its formation. 



But few observations offer themselves respecting the concamerated 

 shell of this fossil. That its first chamber was the testaceous receptacle 

 of an animal, which in all probability was enabled, by its connec- 

 tion with the siphuncle, to vary its situation in the water, appears to be 

 universally admitted. The siphuncule, in the specimens which I pos- 

 sess, pass through the side of the septa ; and this is, I believe, always 

 the case. 



With respect to the enclosing brown spathose part, which is formed 

 by radiating crystals, intersected concentrically, this is found to vary in its 

 figure so much, as to authorize the assumption of such specific dif- 



