74 UNIVALVES. 



species (Bulla Ovum) bears a very striking re- 

 semblance to a Cypreea, it differs chiefly from 

 that genus by the absence of teeth on the colu- 

 mellar lip. Some of the Bullse are remarkable 

 for having both ends of the mouth produced into 

 long beaks; these shells are called birostrate.* 

 (Bulla Volva.) f 



The inhabitants of many of the Bullee are larger 

 than their shells, in consequence they cannot 

 wholly recede into them ; indeed in many the usual 

 order is reversed, and the shell is so surrounded by 

 and enveloped in the body of the animal, that no 

 part of it is visible, and an inexperienced person 

 would little expect to find a regular testaceous 

 specimen buried in an unsightly slug. 



A very remarkable circumstance in the animal 

 of the Bulla, is the form and structure of the 

 stomach, which is furnished with a gizzard ; this 

 organ is composed of three strong shelly pieces, 

 which have a roughness and prominency in their 

 centre, that fits them to grind whatever comes 

 under their action ; these plates are surrounded 

 and connected by a cartilaginous ligament by 

 which they are moved. It is supposed that such 

 a structure is necessary to the existence of these 

 mollusks, from their being exceedingly voracious ; 

 the animal of Bulla aperta has been found quite 



* The children being acquainted with the words rostrum 

 and bis, will see at once the derivation and meaning of this 

 word. 



t Plate II. fig. 8. 



