100 
ROOM XIII. Ricinula , Oliva , Ancillaria Columbella , Nassa, Terebra , 
NatThist. and Buccinum, which are severally distinguished from each 
other by the form of the mouth: some of these, which have 
the lips much dilated over the base of the last whorls, 
have a very large foot, which secretes the shelly matter 
of which the lips are formed. In the Ancillarice , where 
the shell is almost sunk in the foot, its surface is co¬ 
vered w 7 ith a coat of shining enamel. There is also 
in Case 27, a specimen of Terebra , which has had the 
outer part of the shell cut away, to shew 7 the form of 
the pillar, and the mode by which the animal renders 
the tip of the shell solid, by filling it up with a glassy 
secretion. 
In Cases 28—30 are arranged the family of Cowries 
( Cyprceidce .) These shells, w 7 hen young, have a wide 
mouth ; the back is simple and covered with a perios- 
tracum, but as they reach the adult age the mouth is 
contracted, and the back covered with a coat of ena¬ 
mel, deposited on it by the sides of the mantle, which 
becomes expanded for this purpose; as in the genera 
Cyprcea , Algoa , Cyprovula , Trivia , Erato , and Ovula y 
which differ from each other in the teeth on the lips, 
and in the structure of the outer surface. 
Cases 81—34. The family of Volutes ( Volutidce) are 
peculiar for their pillar being plaited. Some of these 
shells are covered with a periostracum, and w 7 hen living 
are often more or less sunk into the large foot of the 
animal; as the genera Cymbium , Voluta , and Mitra; 
others, as the Marginellee have thd back of the shell 
covered with an enamel coat, like the Cowries, which 
is deposited by an expansion of the mantle, similar to 
what takes place in those animals. 
The next order of Ctenobranchous Gdsteropodes live 
chiefly on vegetable food, and being destitute of any 
distinct syphon for the passage of water to the bran¬ 
chial cavity, have no canal in front of the mouth of the 
shell; their eggs are membranaceous and often depo¬ 
sited on the surface of other shells; but many of the 
animals are viviparous. 
Case 
