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one end more extravagantly, so as to give the front view of 
the opening end nearly a circular contour. The lower 
figure shows the beaks. 
The Micaceous sand, besides having these and other 
casts, has siliceous and calcedonic ones. That the Silex 
should replace the Lime of the shells is both curious and 
beautiful, and the filling a mold, as it were, with almost 
loose sand, and in looser sand, is not less curious and 
admirable. Whether we shall ever sce these shells so as to 
identify the hinge we cannot tell. The prominence and 
appearance of the beak and parts around over the hinge of 
the shell, looking something like the mandibule of a bird, 
has caused its name. 
