126 
turbed) very likely goes out in quest of 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 dimen- 
sions of the outer walls, both in length and thickness, 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 spathose pai t of the belemnite : a circumstance which by no 
means agrees with Mr. Platt’s conjecture. According to his opinion, 
the upper chamber should agree, in its circumference, with the up- 
per, or widest part of the belemnite ; the body of the belemnite ac- 
quiring 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 circumference 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 
naturalists, 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 recep- 
tacle of an animal, which in all probability was enabled, by its con- 
nection with the siphuncle, to vary its situation in the water, appears 
to be universally admitted. The siphuncle, in the specimens which 
I possess, 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 
