70 UNIVALVES. 



pansions of the mantle completely cover the 

 shell, when the animal goes forth to seek its 

 food ; at the place where they unite, a longitu- 

 dinal line is formed, from its position on the 

 back of the shell, it is called the dorsal * line ; 

 when the wings are so large that they fold one 

 over the other, their place of junction is not 

 marked. The external polish of these shells is 

 owing to their being so frequently covered by 

 the mantle. The animals inhabiting theCypraea, 

 have a fleshy foot with which they crawl, simi- 

 lar to that of the snail ; the head is placed on a 

 neck, and has two finely pointed tentacula, 

 with two eyes situated at their base ; the mouth 

 is a round opening armed with teeth, these latter 

 are not only organs of nutrition, but defensive 

 weapons. The mantle in front forms a kind of 

 tube, which is lodged in the notch of the shell ; 

 through this the mollusk receives the water it 

 breathes. In a state of rest the Cypraete remain 

 buried under the sea at some distance from the 

 shore, but it is said that at full of the moon 

 they quit this retreat and traverse the rocks. 

 They belong principally to the seas of hot cli- 

 mates ; a few species are met with in temperate 

 regions, but these possess not the beauty of 

 colouring displayed by their congeners. f It may 

 generally be observed with regard to shells, that 



* Dorsal, belonging to the back, from the Latin 

 the back. 



f Congener one of the same genus, from Latin con, to- 

 gether, andgenws. * 



