XII INTRODUCTION. 



Having traced the formation of the shell in a 

 land animal, let us now take a subject from the sea, 

 and we shall find that the same end is produced, in 

 a somewhat different manner. Conchologists are 

 indebted to a French naturalist, M. Bruguiere, for 

 some curious observations on the formation of the 

 shell of the cowry, &c. which the Author begs leave 

 to repeat from what he has already published in the 

 second Volume of Zoography. The inhabitant of the 

 cowry, independent of the organs which are common 

 to animals of other univalve shells, has two membra- 

 naceous appendages, or wings, placed on the sides of 

 the body, with which the creature can completely 

 cover itself. These two wings contribute greatly, 

 together with the edge of the neck, or collar, of the 

 animal, towards the formation of the shell, since 

 they furnish the ordinary exterior layers of enamel, 

 upon which we may perceive the marks of the la- 

 minae, or successive coats, whereof all shells are 

 composed. The shape of the exterior layers is 

 different from those situated beneath, which may 

 be considered as a smooth, shining substance, that 

 the animal goes over once, while it is forming its 

 shell, in order to give it the necessary solidity. It 

 is from the body of the animal, or from the edge of 

 its collar, that the inferior part of the shell is 

 formed, or rather the testaceous mould. This mould 

 is generally thin, and very brittle : it is striated lon- 

 gitudinally ; and, as its origin is not different from 



