70 UNIVALVES. 



shell, when the animal goes forth to seek its 

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

 dinal line is formed, which from its position on 

 the back of the shell 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 beautiful polish of these shells is owing to 

 their being so frequently covered by the mantle. 

 The animal inhabiting the Cypraea, has a fleshy 

 foot similar to that of the snail, by means of which 

 it is able to crawl ; 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 mastication, but also 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 Cyprsese 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 climates ; 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 the intensity of their co- 



* Dorsal, belonging to the back, from the Latin doisum 

 the back. 



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

 gether, and genws. 



