UNIVALVE MOLLUSCA. 413 
well protected by the shell; its stomach, which alone fills a great 
part of the cavity of the body, presents the peculiarity, already noted 
in the genus Aplysia, of being furnished with bony pieces, evidently 
intended to grind the food. 
The Bulle can swim with facility in deep water, but they evidently 
Fig. 184.—Bulla oblonga Fig. 185.— Bulla aspersa Fig. 186.—Bulla nebulosa 
(Adams). (Adams). (Gould). 
prefer the shallows and a sandy bottom, feeding upon smaller mol- 
luscs. They are found in every sea, but they abound chiefly in the 
Indian Ocean and Oceania. Some species, however, such as Bud/a 
ampulla (Figs. 182 and 183), the shell of which is shaded grey and 
brown, and the Water-drop (Bulla hydatis), inhabit European seas. 
Bulla oblonga and Bulla aspersa (Adams), and Bulla nebulosa (Gould), 
represented in Figs. 184, 185, and 186, are also well-known species. 
