76 UNIVALVES. 



volutions, but at the top is depressed, and has a 

 small umbilicus ; it is usually about two inches 

 long, and one and a quarter broad at the base. 



This is one of the Bullse which possess a giz- 

 zard.* In this animal it consists of two trian- 

 gular, thin, testaceous plates nearly an inch in 

 diameter, and another of an elongated semi- 

 cylindrical form. These plates are connected 

 together by a tough yellowish ligament ; and 

 form a most powerful digestive organ ; when the 

 animal has been dissected, there have been found 

 in or near this gizzard, numerous specimens of 

 the smaller testacea, with their shells reduced to 

 a complete powder. 



This is the largest species of the British Bullse. 



BULLA FontincdisJ 



STREAM DIPPER. 



Specific Character. Shell sinistral, having four 

 or five reversed volutions, glossy, pellucid, J and 

 of a light horn colour ; the body whorl is large ; 

 the others are very small, and not much pro- 

 duced ; aperture oval oblong, three fourths of the 

 length of the shell. Old specimens are some- 



* Plate II. fig. 7. t Plate II. fig. 9. 



J Pellucid, so clear that the light is seen through it. From 

 Latin, per through, and lux light. 



