BULLA DIPPER. 75 



distorted from its having swallowed entire a shell 

 nearly equal in size to itself. Not unfrequcntly 

 shells are found in the gizzard of these animals, 

 reduced to a complete powder, affording ample 

 proof that it unites the two offices of mastication 

 and digestion. 



The Bullse are not furnished with an opercu- 

 lum ; indeed to many of the species it would be 

 a useless appendage, as the animal extends be- 

 yond 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 mollusks who live near the shore, and bar- 

 ricade the mouth of their shells with their 

 opercula. 



BULLA Lignaria.* 

 WOOD DIPPER. 



Specific Character. Shell oval, thin, brittle, 

 semi-transparent, yellowish or chesnut brown, 

 with numerous transverse striae of a light colour 

 approaching to white, giving it some resemblance 

 to veined wood; sometimes it has one or two 

 oblique bands ; inside white, glossy ; aperture 

 large, extending the whole length of the shell, 

 somewhat contracted towards the upper part ; 

 columellar lip smooth ; it has no external con- 

 * Plate II. fig. 6. 



