UNIVALVES BULLA. 99 



BULLA Dipper or Bubble. 



DESCRIPTION OF PLATE XXII. 



Dnr. L(— Fig. 3. B. verrucosa. Div. III. — Fam. 2. Fig. 5. B. amplustre. 



Div. II Fig. 1. B. volva. Dit. IV — Fig. 7. B. ficus. 



Fig. 2. B. gibbosa. Drv. V. —Fig. 6. B. virginea. 



Drv. VI.— Fig. 4. B. terebelluin. 



Shell univalve, convolute, unarmed with teeth; aperture a little 

 straitened, oblong, longitudinal, very entire at the base ; pillar 

 oblique, smooth. 



THIS genus is so nearly allied in form to the preced- 

 ing, that much caution is necessary in order to prevent 

 confusion in its classification; so great indeed is the 

 difficulty of distinguishing the young shells of the 

 Bulla and Cyprsea, that the two genera have been in- 

 termixed by some authors. 



This difficulty may, however, in a great measure be 

 removed, by an attention to one very striking charac- 

 ter of the Bulla, that the pillar lip of the shell, in 

 every state of its growth, is invariably free from the 

 slightest denticulations ; while, in the Cyprsea, both 

 the pillar and outer lips are crenated with strong ar- 

 ticulated or prominent teeth. This distinction consti- 

 tutes the character of the first of the divisions, into 

 which the genus is separated. The other divisions are 

 in general distinguished by the form, of which the Bulla 

 presents a considerable variety. The second division 

 comprehends the species which are elongated : in these 

 the length is increased by two produced beaks, con- 

 spicuously observable in the B. volva. In the third di- 

 H2 



