BULLA. 



The Bullae are generally oval, more or less spirally 

 convoluted univalves, sometimes having a distinct, though 

 short spire, and not unfrequently a depression in place of 

 the spire : they are mostly thin, and generally varied in 

 their coloration, though occasionally of an uniform colour 

 and sometimes even colourless ; aperture generally large, 

 and nearly as long as the shell, for the most part longi- 

 tudinal, though sometimes almost transverse, in most 

 species wide and much wider anteriorly or at the lower 

 part than at the upper, in some instances very wide and 

 spreading, and very seldom narrow and almost linear, 

 always effuse at the lower extremity. On one side the 

 Genus Bulla appears to approximate in general appearance 

 to Tornatella, some of its species, the B. Amplustre, for 

 example, having nearly the same form ; and on the other 

 side to the Aplysiadae, the B. aperta approaching very 

 nearly in form to the Dolabell^. A circumstance remark- 

 able in the animal of the Bullae is the form and structure 

 of the stomach, which in most of them consists of three 

 strong shelly pieces united by powerful adductor muscles ; 

 we suppose such a structure to be necessary to their 

 existence, for they are exceedingly voracious as is evident 

 from the fact that the animal of B. aperta is sometimes 

 distorted by having swallowed entire a Corbula Nucleus, 

 which is a very thick and strong shell, nearly equal in size 

 to itself. 



The Bullae are marine, and they appear to belong to 

 nearly all climates; several are common on our own 

 coasts ; very few of them grow to be so large as a Walnut 

 and they are for the most part much smaller. Fossil 

 species are only to be distinguished in the tertiary beds 

 and in the green sand. 



In our plate we have given representations of 



Fig. 1. Bulla aperta, (Bullsea, Lam.) 



2. —— virescens, nobis. 



3. Li{fnaria. 



4. Ampulla. 



5. ' - • calyculata. 



6. \ - I Physis. 



7. — ^ — cylindrica. 



8. Amplustre. 



