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side. A further examination with a lens, assisted in explaining this 
circumstance ; since I thereby discovered, that the whole internal sur- 
face was beautifully frosted over with minute crystals of calcareous 
spar, which had most probably concealed the lines of attachment. 
The operculum is sometimes convex, but in general it is concave. 
It is for the most part firm and solid, except on its upper part, where 
innumerable foramina are observable ; being the openings of minute 
tubuli, which appear to enter into the composition of its superior part. 
Two larger openings are also observable, which, in their figure and 
situation, appear to correspond with the two internal ridges. Picot 
examined numerous specimens, with the hope of ascertaining the mode 
in which this operculum joined the mouth of the shell, not doubting 
that it was attached to the animal, who possessed the power of opening 
and of shutting it at pleasure. He found in every instance, that the 
edges of the opercula were so exactly adapted to the openings, as to 
allow of their being thus completely closed. In one instance only he 
found two projecting pieces on the lower surface of an operculum, 
which had somewhat of the appearance of the remains of an hinge ; 
but never having observed any thing similar on any other specimen, 
he is disposed to conclude that this appearance was accidental. 
Of the particular economy of the animal which inhabited this shell, 
we cannot form any correct opinion from the specimens which have 
been yet made known : nor can any satisfactory opinion be formed 
respecting the action of the operculum, or the use of the lateral lidges, 
until more perfect specimens have been discovered. Until then, also, 
must be deferred, the attempt to determine the specific distinctions of 
these fossils. 
The Abbe Fortis appears to have met with some fossil bodies in Dal- 
matia, which might, perhaps, be classed among the hippurites. “ Walk- 
ing/’ he says, “ about the habitations of Rogosniza, I happened to dis- 
cover, in the hard marble rock, a curious fossil, very much resembling 
horns ; and recollect to have observed, in the public Museum of Natural 
