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surround the mouth of the shell : a discovery which cannot fail to 
throw light on the economy of many of the inhabitants of the minute 
multilocular shells. Lamarck considering that, agreeable to the dis- 
coveries of M. Peron, three fourths of the shell of Spirula is covered 
bv the animal, and that there is great reason to suppose that one third 
of the shell of the Nautilus is also thus covered, is of opinion, that 
the nummulite was completely inclosed in the posterior part of the 
animal by which it was formed ; and that a part of the extremity of 
the animal was contained in, and was adherent to, the last chamber. 
Possessing several small masses of these bodies, and having been 
careful in collecting all the different surfaces and forms under which 
these bodies presented themselves, in different specimens, I made a 
careful examination of them, with the hope of obtaining some more 
particular information respecting their original nature. 
The size of the specimens, which I possess, vary in their diameter, 
from less than an eighth of an inch to an inch and a quarter ; and I 
am satisfied, that I once had some which were full an inch and a half 
in diameter. In thickness, they vary from an eighth of an inch to 
half an inch. 
Their figure is in general lenticular. Considerable variations, 
however, are frequently observable in this respect ; the lens, from 
what has been stated in the preceding paragraph, being much deeper 
in some than in others : some, indeed, being nearly flat, whilst others 
are even almost globular. In some, a considerable deviation appears to 
have taken place from their original figure, from their having become 
bent in various ways. The surface varies considerably in different 
specimens ; being in some nearly smooth, in others rough and 
scabrous, with numerous small projecting knobs, or undulating lines. 
Their colour is also various ; some being white, some of different 
shades of brown and red, and others even of a blueish hue ; and the 
difference of colour is certainly not always dependent entirely on the 
nature of the matrix in which they have been imbedded. The number 
