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 Bullae can swim with facility in deep water, but they evidently 



Fig. 184. — Bulla oblonga 



(Adams). 



Fig. 185.— Bulla aspersa 

 (Adams). 



Fig. 186. — Bulla nebulo-sa 

 (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 Bulla 

 ampulla (Figs. 182 and 183), the shell of which is shaded grey and 

 brown, and the Water-drop {Bulla /lydatis), inhabit European seas. 

 Bulla oblo?iga and Bulla aspersa (Adams), and Bulla nebulosa (Gould), 

 represented in Figs. 184, 185, and 186, are also well-known species. 



