S2 UNIVALVES. — BULLA. 



young being produced from eggs. The reverse varieties 

 (that is to say, those having tlieir whorls or spires twist- 

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

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

 valued. The Bulla purpurea inhabits Africa, and is 

 found in rice-fields. 



The snail-shaped Bullgp, such as the fasciata, virginea, 

 &c. &c. are most beautifully banded with parti-colored 

 streaks ; they are found in the yivers of Asia. The Bulla 

 gelatinosa, is an inhabitant of the rivers of Denmark; 

 the fontinalis is found in the Danube, and other species 

 inhabit various lakes and rivers of Europe: in wet mea- 

 dows, among moss, they are also to be met with. Some 

 species of this genus are remarkable for the brittleness 

 and lightness of their shells; such are the Bulla velum, 

 vesica, &c. &c. 



The inhabitant of one of the species. Bulla lignaria, 

 and, in all probability, those of most of the genus, is fur- 

 nished with an organ resembling the gizzard of a fowl, 

 and which it appears to use for the purpose of masticat- 

 ing its food. 



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 caused by the rain. 



BULLA.— Dijyper. 



Ovum {Poached Egg.) Birostris {FalseWeavers S.) 



Volva ( Weavers Shuttle.) Spelta {Oblong D.) 



