MOLLUSCA. 101 



As originally constituted, the genus of Linnaeus contain- 

 ed species of very different characters, so that many new 

 genera have been formed. To Bruguiere, Lamark, and Dra- 

 parnaud, we owe all the improvements which have taken 

 place. 



The modern genus BULL A includes those shells which cor- 

 respond with the following character : " Testa univalvis, 

 convoluta, ovato-gibbosa vel cylindracea : spira non exserta, 

 apertura longitudine testae, labro acuto." The B. ampulla 

 is the type of the genus. 



The genus O VUL.A, instituted by Bruguiere, is more nearly 

 related to the cyprea than to the bulla. It differs, however, 

 from the former, in the left margin of the lip being smooth ; 

 and from the latter, in the edges of the mouth being'rolled 

 inwards, and in the shell being produced at both ends. The 

 B. ovum of Linnaeus is the type of the genus; the B. patula 

 of Pennant. 



" The bulla terebellum has been employed by Lamark to 

 constitute his genus TEREBELLUM. The canal at the base 

 of the mouth, and the truncated pillar, furnish the generic 

 characters. 



Linnaeus was for some time uncertain where to place those 

 shells which he at last inserted in the genus bulla, under the 

 trivial names ficus and rapa. These, with a few of the mu- 

 rices of the same author, constitute the genus PYRULA of 

 Lamark. Its canaliculated base removes it from the bullae, 

 while the short spire, the swelling of the last whorl, thp 

 smooth pillar, and pyriform shape, distinguish it from all 

 those with which it is apt to be confounded. It is more 

 nearly allied to the Fusus than to any other. 



The preceding genera consist of species which live in the 

 sea. The B. virginea is a terrestrial shell, and ought to 



