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 Linneeus, and probably belongs to this 
genus. 
In the genus Oxtva, the turns of the spire are separated 
externally by a very distinct gutter or canal, and the pillar 
is obliquely striated. The voluta oliva of Linnzeus contains 
many different species of this genus, which are remarkable 
for the smoothness of their surface and the brilliancy of their 
colours. 
The Ancriua, 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 Mrrra of Lamark, the spire is pointed in- 
stead of ending in a small knob, as in voluta, and the plice 
of the pillar increase in size from the base upwards, which 
isthereverse in that genus. The V. episcopalis of Linneeus is 
the type of this genus, which contains many species much 
sought after by collectors. 
In the CoLtuMBELLA, the shell is oval, the spire short, 
and the inner edge of the right lip is swollen. The V. 
mercatoria is the type of the genus. 
The 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. glabelia is the type of the 
genus. 
The CancELLaARrtia is nearly related to the genus colum- 
bella, but the absence of the swelling of the lip, and the 
presence of the compressed sharp plice of the pillar, furnish 
