120 



side. A further examination with a lens, assisted in explaining this cir- 

 cumstance ; since I thereby discovered, that the whole internal surface 

 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 doubt- 

 ing that it was attached to the animal, who possessed the power of open- 

 ing 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 ridges, 

 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 disco- 

 ver, in the hard marble rock, a curious fossil, very much resembling 

 horns; and recollect to have observed, in the public Museum of Natural 



