MOLLUSCA. 103 



Costa, as if they were one and the same. But Pennant's 

 shell is a true bulla, while that of Da Costa is regarded as 

 the voluta pallida of Linnaeus, and probably belongs to this 

 genus. 



In the genus OJLIVA, the turns of the spire are separated 

 externally by a very distinct gutter or canal, and the pillar 

 is obliquely striated. The valuta oliva of Linnaeus contains 

 many different species of this genus, which are remarkable 

 for the smoothness of their surface and the brilliancy of their 

 colours. 



The ANCTLLA, which, like the former, is of a sub-cylin- 

 dric form, is destitute of the groove which separates the 

 whorls, and is characterised by an oblique callous ring at 

 the base of the pillar. 



In the genus MITRA of Lamark, the spire is pointed in- 

 stead of ending in a small knob, as in voluta, and the plicae 

 of the pillar increase in size from the base upwards, which 

 is the re verse in that genus. The V. episcopalis of Linnaeus is 

 the type of this genus, which contains many species much 

 sought after by collectors, 



In the COLUMBELLA, the shell is oval, the spire short, 

 and the inner edge of the right lip is swollen. The V. 

 mercaloria is the type of the genus. 



Th.e MARGINELLA is very distinctly marked by the pro- 

 minent callous collar which surrounds the outside of the 

 right edge of the shell. The opening of the mouth at the 

 base is scarcely grooved. The V. glabella is the type of the 

 genus. 



The CANCELLARIA is nearly related to the genus colum- 

 bella, but the absence of the swelling of the lip, and the 

 presence of the compressed sharp plicae of the pillar, furnish 



