BULLA DIPPER. 77 



of two or three plates, sometimes of a corneous,* 

 and sometimes of a testaceous nature ; these 

 plates have a roughness and prominency in 

 their centre, by which they are fitted to grind 

 whatever comes under their action ; they are 

 surrounded and connected by a cartilaginous 

 ligament by which they are moved. This giz- 

 zard appears an extraordinary organ for such 

 an animal to possess, but upon dissecting these 

 mollusca, small shells have been frequently 

 found in their gizzard, and even the testaceous 

 matter reduced to a powder, affording ample 

 proof that it unites the two offices of mastication 

 and digestion. 



The Bullae are not furnished with an oper- 

 cuium ; indeed to many of the species it would 

 be a useless appendage, as the animal extends 

 beyond the shell, and cannot, on account of its 

 gizzard, contract itself so as to retire within. 

 The marine species also reside in deep water, 

 and they are as safe there from crabs and other 

 enemies as the mollusca who live near the shore, 

 and barricade the mouth of their shells with their 

 opercula. 



BULLA LignariaJ 

 WOOD DIPPER. 



Specific character. Shell oval, thin, brittle, 

 semi-transparent, yellowish or chestnut brown, 



* Corneous, horny, from the Latin cornu, a horn, 

 t Plate II. fig. 6. 



7* 



