94 INTRODUCTION TO CONCHOLOGY. 



of the animal ; it is not, however, covered by the mantle, 

 but rather protected by a modification of the disc. The 

 mantle itself is limited to the interior and aperture of the 

 shell : it appears to be farled over the edge of the lip, and is 

 held, as it were, in a state of tension by a cord or filament, 

 passing from the posterior extremity into a deep, narrow 

 channel, excavated round the spire of the shell, in place of 

 the suture. The result of this difference in the calcifying 

 organ is extremely curious. In the Cowry the testaceous 

 fluid is deposited from the outside in layers, at different 

 intervals ; in the Olive, it is secreted in layers simultaneously 

 at the lip, and the porcellaneous surface of the shell is 

 preserved in its difi^erent stages of growth^ as well as after 

 its maturity, by a reflection of the ventral disc, in a manner 

 somewhat analogous to the reflected mantle of the Cowry ; 

 having nought to do with the formation of the sliell, how- 

 ever ministering to its preservation by the tendency of its 

 viscid humour. 



Every period in the life of a Cowry, as already noticed, 

 is designated by a different design of colouring. It is 

 otherwise with the Olive, which uniformly exhibits the same 

 appearance from youth to age : different layers of colouring 

 matter must consequently be deposited at the same time. 



