102 
ROOM XIII. expanded, flat, and orbicular, and as large as the mouth 
Nat. Hist, of the shell, which is generally protected by a horny oper¬ 
culum; as the genera Vermetus and Spiroglyphus. The 
family of Capulidcz have a simple conical shell. They 
are always attached to rocks by the back of the foot 
of the animal, which is folded on itself and unfit for 
walking upon. This back of the foot either secretes a 
shelly plate like an operculum, or forms a depression in 
the surface of the body to which it is attached, of the 
size of the shell, and marked with a crescent-shaped 
ridge, shewing the places where the muscle was fixed; 
as the genera Capulus and Hipponyoc. Lastly, the 
family of the Crepidulce , (Crepidulidce ,) which have 
a very large and expanded mouth, and the inner 
lip very small and thin ; the latter is even sometimes 
entirely wanting; they have no operculum, and their 
gills form an oblique band across the front of the 
neck, as in the genera Crepidula , Calyptrcea , Cremoria , 
and Dispotea: at the end of this family may be placed, 
till the animals and their habits are better known, the 
genera Velutina and Phorus. The latter are peculiar 
for attaching to the outer surface of their shell, as it 
increases in size, stones, or fragments of other shells and 
corals; from whence they have been called respectively 
the Conchologist and the Mineralogist. The Phori 
have a subannular operculum, very like that of the 
Buccinum. 
Cases 42—48 contain the third order of Ctenobran- 
clious Gasteropodes, which are herbivorous, and have 
an entire mouth to their shells like the former, but, like 
the snail, they are hermaphrodite. The sides of' the 
body are furnished with a series of filaments. Many of 
these have spiral shells, which are of a pearly lustre 
internally; as the family of the Turbines, ( Turbinidce ,) 
which have a rounded mouth and a shelly operculum, as 
the genera Turbo , Imperator , and Phasianella. The 
family of the Trochi ( Trochidce) have a square mouth 
and horny spiral operculum; as Trochus , Rotella , 
Monodonta and Solarium . The family of the Earshells, 
(Haliotidee,) 
