442 THE OPERCITLUM. 



Oliva or an Ancillaria, were each and all deposited by some 

 expansion of the mantle. 



I have lately, however, had an opportunity of observing 

 the animals of all these, and of many other genera, in the 

 Museum of the Jardin du Roi at Paris, where my excellent 

 friend Professor De Blainville, who was at that time keeper 

 of this part of the collection, kindly allowed me to examine 

 at my leisure all the stores of Mollusca collected together 

 during a long series of years by the late Baron Cuvier, as 

 well as those brought home by MM. Quoy, Gaimard, and 

 Lesson, from the recent voyages of discovery in which those 

 naturalists took part. At the same time I was allowed, by 

 the kindness of M. Quoy, to consult and copy the numerous 

 drawings made by him, during his voyage, from the animals 

 whilst alive and in motion. From this examination I am 

 enabled to state, that in all the shells just named the shelly 

 matter in question is deposited, and most probably secreted, 

 by the upper surface of the foot, which is very large, and 

 not by the mantle, which, on the contrary, is small, and not 

 expanded beyond the edge of the mouth. This is most 

 obviously the case in the Cymbia, Olivse and Ancillariae, 

 which have so large a foot that the shell appears to be actu- 

 ally immersed in it. Animals of these genera, drawn from 

 life, are figured by Adanson in his Voyage to Senegal, and 

 by Forskahl in his Fauna Arabica. The Murex anus of 

 Linnaeus, which has been referred by Lamarck to his genus 

 Triton, differs in this particular from all the other animals 

 placed by him in that group, and agrees with the genus 

 Cassis, the expanded base round the mouth being produced 

 by the very widely expanded foot : it forms the genus Per- 

 sona of De Montfort. 



It is remarkable that this fact should not have been before 

 observed, more especially as the operculum of all molluscous 

 animals which are furnished with such a protection is secreted 

 by the back of the hinder part of the foot, where there is 

 no extension of the mantle. 



6. On the Operculum. 



The part usually called Operculum is a horny or shelly 

 plate, adherent to the back of the hinder part of the foot 

 of many gasteropod Mollusca. It is always (except, per- 

 haps, in Navicella) attached to the free end of the large 

 muscle by which the animal is affixed to its shell ; by the 

 contraction of which the operculum is brought into such a 

 situation as more or less completely to close the mouth of 



