102 CONCHOLOGY. 



account of the shell being entirely covered by the animal, and 

 never externally visible. 



Shell oval, thin, fragile, more or less involuted on one 

 side, rendering the aperture more or less wide. 



B. aperta. The open BuUaea. PI. 17, fig. 5. 



Shell interior and very incompletely involuted, without 

 spire or columella ; sub-orbicular, white, transparent, faintly 

 striated, and slightly wrinkled ; almost entirely open. 



3. Bulla. The Bubble. Eleven species. 

 The great confusion that existed in this genus, as classed 

 by Linnasus, has been elucidated by the division and classi- 

 fi.cation of Lamarck. This genus derived its name from the 

 resemblance which some of the smaller species have to a 

 bubble of water. Its shells are found in almost all parts of 

 the world. 



Shell externa], oval, involuted ; aperture very large, open 

 the whole length of the shell, and generally wider at the 

 base ; outer edge sharp and smooth ; summit umbilicated. 

 Bulla lignaria. Bulla fasciata. 



B. ampulla. B. aplustre. 



B. striata. B. hydatis. 



B. naucum. B. cornea. ' 



B. physis. B. fragilis. ' 



B. solida. 



B. aplustre. The streamer-like Bulla. PI. 17, fig. 7. 



Species completely involute ; the spire very distinct, vis- 

 ible, but not projecting, with a kind of thickening at the an- 

 terior part of the columellar edge. 



B. lignaria. The woodlike Bulla. 



Species sub-involute, no visible spire either within or with- 

 out, but narrowed towards the top when it is slightly umbili- 

 cated ; yellowish brown colour, with transverse pale striae. 



B. hydatis. The watery Bulla. 



Species more solid, thicker, almost entirely involute ; 



