85 
ROOM XIII.] NATURAL HISTORY. 
lip generally granular; and the Mask shell, (Persona,) 
with the base expanded into a disk; others have the inner 
lip smooth as those of the true Murices, or Rock shells. 
Some have only indistinct varices, or none at all, as the 
genera Pleurotoma, Conus, Fusus , and Pyrula , which 
have the pillar smooth ; Turbinellus, Fasciolaria, and 
Cancellaria, which have this part plaited like the Volutes; 
amongst these may be observed a very fine specimen of 
the reversed Chank shell, highly valued by the Chinese. 
Cases 20 to 27 contain the family of the Buccina, 
(Buccinidce ,) which have either an elongated and reflexed, 
or short, curved canal in front of the mouth ; and include 
the genera Cassis, Dolittm Harpa, Purpura , Magilus, 
Ricinula , Oliva, Ancillaria, Columbella, Nassa, Terebra, 
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 covered with 
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 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, when young, have a wide 
mouth; the back is simple and covered with a periostra- 
cum, but as they reach the adult age, the mouth is con¬ 
tracted, and the back covered with a coat of enamel, de¬ 
posited on it by the sides of the mantle, which becomes ex¬ 
panded for this purpose ; as in the genera Cyprcea , Algoa, 
Cyprovula, Trivia, Erato, and Ovula, which differ from 
each other in the teeth on the lips, and in the structure of 
the outer surface. 
Cases 31—34. The family of Volutes (Volutidce) are 
peculiar for their pillar being plaited. Some of these 
shells are covered with a periostracum, and when living 
are often more or less sunk into the large foot of the 
animal; as the genera Cymbiuw , Voluta , and Mitra; 
others, as the Marginellce, have the back of the shell 
covered with an enamel t, like the Cowries, which is 
