ROOM XIII.] 
NATURAL HISTORY. 
87 
Case 41 contains the shells of those Mollusea of this 
order, which are peculiar for having their branchiae formed 
of very long filaments, as the family of Worm Shells, 
( Vermetidce ,) which are often attached by the outer surface 
to marine bodies; being thus fixed, the foot is not fur¬ 
nished with a distinct disc for walking, but its end is ex¬ 
panded, flat, and orbicular, and as large as the mouth of 
the shell, which is generally protected by a horny opercu¬ 
lum; as the genera Vermetus and Spiroglyphus . The 
family of Capiilidce 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. Tni&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 Capulits 
and Hipponyx. Lastly, the family of the Crepidulos , 
(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 oper¬ 
culum, and their gills form an oblique band across the 
front of the neck, as in the genera Crepidula, Calyptrcea , 
Cremoria , and Dispoteci : at the end of this family may be 
placed, till the animals and their habits are better known, 
the genera Velutina and Pkorus. The latter are peculiar 
for attaching to the outer surface of their shell, as it in¬ 
creases 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- 
chous Gasteropodes, w T hich 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, ( Turbinidoe ,) 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 , Eotella , Monodonta and Solarium . 
