76 LESSON XI. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



This genus is perhaps less accurately defined 

 than any other of the Linnaean Genera : it con- 

 tains an assemblage of shells presenting a very 

 varied appearance ; indeed it seems as if it had 

 been formed to be a receptacle for including all 

 the species that could not find a place in other 

 genera. The most distinguishing characteristic 

 of the Bulla is its gibbous or inflated figure, to 

 which it owes its name, signifying water bub- 

 ble. One species (Bulla Ovum) bears a very 

 striking resemblance to the Cyprsea, it differs 

 from that genus only by the absence of teeth on 

 the columellar lip. Some of the Bullse are re- 

 markable for having both ends of the mouth pro- 

 duced into long beaks ; these shells are called 

 birostrate.* 



The inhabitants of many of the Bullse are 

 larger than their shells, so that they cannot wholly 

 recede into them ; indeed in many the usual 

 order is reversed, and the shell is so surrounded 

 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 forma- 

 tion of many of the animals of this genus, is that 

 they are furnished with a gizzard to masticate 

 and digest their food. This organ is composed 



* The children being acquainted with the words rostrum and bis, 

 will see at once the derivation of this word. 



