258 SUPPLEMENT 
it is small, asin the vis, &c. It may be very much elongated, 
as for example in the cypreade. It is formed entirely by the 
aperture in the patella and some others, and at other times by 
a portion of the last turn of the spire. 
Its direction, which is usually that of the aperture, also pre- 
sents some considerations which ought not to be neglected : 
thus, it is altogether perpendicular to the axis of the shell in 
the patella, &c.; and it is almost entirely in its direction in 
the cypree and olivi. The other shells are more or less inter- 
mediate. 
The body of the shell is all that portion which is between 
the basis and the head. Most frequently it is hollow in the 
interior, and serves not only to cover the body of the animal 
on its upper part, but also to contain a greater or less portion 
of it. 
Sometimes it receives the name of discus, as in the halio- 
tides; but then only the last turn of the spire is comprehended 
under this name. 
In a certain number of shells or teste, the body is curved in 
no direction, neither to the right, nor to the left, nor in front, 
nor in rear, and is even in no wise excavated. These are 
named flat shells, symmetrical in the bone of the sepia and 
the calamary, non-symmetrical in the patella Sinensis. 
Pretty often the base and summit are united by a body 
which is not recurved in any way, but which is more or less 
excavated. This constitutes the covering or sheathing shell, 
as in the patella, the emarginule, and especially in the den- 
talia. 
Finally, in many cases the body of the shell is formed by its 
enrolment in different ways. Such it is in the true coch- 
lide or spirivalves. , 
To form a just idea of this, we may conceive that every uni- 
valve shell was a cone more or less elongated, but flexible. 
If it be rolled from rear to front, and from top to bottom, 
a ee ee 
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