88 UNIVALVES. — BULLA. 



Some of the Bullae, as the B. ficus and B. rapa, are very 

 similar to the gemis Murex : the latter species is esteemed 

 a rarity; the former, on the contrary, is common, and very 

 much resembles the shape of a fig. 



The B. zebra, B. fasciata, B. achatina, and other simi- 

 lar species, are land shells ; in form, they are nearly allied 

 to the genus Helix. It is remarkable, that the animals 

 which inhabit them are oviparous. The reverse varieties, 

 that is to say, those having their whirls or spires twisted 

 contrary to the usual direction, and having, at the same 

 time, their mouths placed on the opposite side, are highly 

 valued. The B. purpurea inhabits Africa, and is found in 

 rice fields. 



Some species of this genus are remarkable for the brit- 

 tleness and lightness of their shells; such are the B. velum, 

 B. amplustre, &c. 



The inhabitant of the B. lignaria, and, in all probability, 

 of many other species, is furnished with an organ called a 

 gizzard, of a testaceous nature. 



The different species of this genus are to be found in the 

 Mediterranean, African, American, Indian, European, and 

 Northern seas. 



The Bulla, probably, derives its name from some of the 

 lesser species resembling a dew-drop, or bubble of water. 



BULLA— Dipper. 

 Division I. — Shell resembling the cypr^ea genus, but 



TOOTHED ON THE OUTER LIP ONLY. 



Ovum — Poached-egg. Nucleus — Wrinkled. 



Imperialis — Crumpled. Verrucosa — Warty. 



Division II. — Shell oblong, beaked at the ends. 



Volva — Weaver's-shuttle. Secale — Rye-shaped. 



Lepida — Orange. Spelta — Ohloyig. 



Birostrls — Lesser. Gibbosa — Belted. 



