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sometimes larger, when the hinge does not seem to occupy 
so large a proportion of the shell as in the smaller ones. 
Although I do not understand that there are any recent 
shells of this species, yet the habitat might not be thought 
Ter y antient, as the shell is apparently but little changed 
from its original substance or structure. The specimens 
are said to be very small in the neighbourhood of Paris, 
and large at Piedmont and Florence. My figure is a little 
diminished from one about four inches and an half wide. 
The old and larger shells seem worn on part of the hinge, 
and the teeth at the edge are almost obliterated, their form 
is short and broad; the ribs extend most on the shorter 
side of the shell, and do not reach to the margin as in the 
smaller ones: the laminated structure of the older shells 
admits of the outer coat breaking off, so as to show the 
space between the ribs nearly equal to the ribs and flat, 
while the furrows in the upper coating are much con® 
tracted, ending acutely, when they meet the more pro® 
xninent transverse striae of growth near the margin. The 
whole is nearly smooth and greyish, stained with darker of 
lighter ochraceous Iron, &c. 
