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boundary, whilst a straight elongated fragment lies within, 
and rests its ends against the line of granular matter (as 
shown by Fig. 6). Hence it appears that both the finer 
matter and the larger extraneous fragment rested originally 
on the inner surface of a shell that has become crystalline. 
The thickness of the shell shown by both these specimens 
was about Tuocjth of an inch, which is so thin that we could 
not expect to find any trace of it in the agate, when the 
septa of the ammonites are obliterated. These facts, I 
think, indicate that these bodies were small shells, whose 
interiors have been filled with calcareous or siliceous in- 
filtrations, in the same manner as the chambers of the 
ammonites which are found in the rock. Nevertheless, I 
will not insist on this view, for I have found cases where 
the impurities were not arranged as if there had been a 
shell, though not in a manner irreconcilable with that suppo- 
sition ; but, on the whole, I should say, that there is better 
reason for thinking them to have been shells, than any other 
bodies with which I am acquainted. If really shells, they 
may perhaps have been Foraminifera, although I have not 
been able to detect any internal divisions into chambers, 
nor anything to indicate that they are detached forami- 
niferous cells, such as are sometimes met with. 
Besides the reniform bodies, we find in the matter left 
undissolved by acid several other minute agatized organic 
bodies, which it may, perhaps, be as well to describe. There 
occur minute cellular bodies (zoophytes?) formed of more 
or less oval open cells, concave on one side and convex on 
the other, placed end to end, and communicating at the 
extremities, in a similar manner to what is seen in the 
section of a Nodosaria. The cells are frequently irregular, 
and vary much in form ; two or more rows being often placed 
side by side, and single rows of cells frequently branch off 
from the main body. 
