112 
NATURAL HISTORY. [EAST. ZOOL. 
shelly matter of which the lips are formed. The Olives 
have the shell covered with a polished coat, and sunk into 
the large expanded foot, so that only a small part of its 
hack can be seen when the animal is walking; the front 
of the foot is separated from the hinder part, as in the 
Volutes,*by a deep nick on each side, and the front of the 
pillar of the shell isobscurely plaited. The true Olives 
{Oliva) have 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 An - 
cillarice . 
The family of Volutes ( Volutidce, Case ) have a re¬ 
curved 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, Valuta , 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 angulala , 
one of the sides, and in others, as Mar gin ell a, 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, Case ) 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 tnantle 
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 
