87 
EAST. ZOOL. GAL.]] NATURAL HISTORY. 
a canal round the suture of the whorls,, formed to inclose a 
filiform process arising from the hinder end of their small 
inclosed mantle* which is wanting in the Ancillarice . 
Most of these genera are provided with a distinct oper¬ 
culum* except Harpa, the larger species of Olives, and 
the Ancillarice . 
The family of Volutes ( Volutidce, Cases 12—14) have a 
recurved syphon* and only a nick in the front of the mouth 
of the shell* like some of the former genera; but the front 
of the pillar of the shell is regularly and obliquely plaited. 
The foot of the animal is very large, partly hiding the shell* 
and generally deeply nicked on each side in front. In 
general the shell is covered with a distinct periostraca* as 
Mitra, Volnta * and Musica * but in a few* as Cymbium , 
the animal* when any sand or other matter gets between 
the shell and the upper surface of its foot* secretes a 
quantity of shelly matter* and covers the adventitious sub¬ 
stance with a glassy coat* so as to prevent the extraneous 
particles from irritating it. In some* as Voluta angulata * 
one of the sides* and in others* as Marginella , both sides 
of the mantle* are produced and reflected over the back of 
the shell, and the shelly matter secreted by these parts 
covers the outer surface of the shell with a polished coat, 
like the Cowries. Only a few species* as Voluta musica * 
and some of the smaller Mitres * are provided with a horny 
operculum* which is entirely deficient in the other kinds. 
The animals of the genus Cymbium are ovoviviparous; the 
shell of the newly born animal is very large* and the apex 
of the spire of many of these shells is very irregularly 
twisted. 
The family of Cowries ( Cyprceadce * Cases 15* 16) in the 
young state have a thin shell* covered with a thin peri¬ 
ostraca* and with a wide mouth like that of Bulla * but* 
as they approach the adult age* the lobe of the mantle 
spreads out so as to cover the back of the shell with two 
large lobes* which are capable of being contracted into the 
cavity of the shell at will; at the same time the mouth of 
the shell is gradually contracted and indexed* only leaving 
a narrow slit* and its back is covered with an enamel coat, 
deposited on. its sides by the lobes of the mantle* the 
foot is rather small. The outer surface and edge of the 
lobes of the mantle are generally covered with various 
shaped and often branched beards. In Cyprcea * Luponia, 
