288 THE INHABITANTS OF THE SEA. 
The Pectinibranchiata comprise all the spiral univalve shells, 
and are by far the most numerous of all the gasteropods, as their 
species are not counted by hundreds, but by thousands. If their 
caleareous garment could be drawn out, it would be found to 
consist of a tube gradually widening from the apex to the base; 
but what an immense variety of form and ornaments, what a 
prodigality of splendid tints, has not Nature spread over this 
interminable host! The same fundamental idea appears to us 
in thousands of modifications, one yet more elegant and capricious 
than the other. Thus the passion of the 
shell collector is as conceivable as that of 
the lover of choice flowers, and when we read 
/ that rich tulip-amateurs have given thousandg 
& 
FX 
of florins for one single bulb, we cannot won- 
der that many of the Volutes, Cones, Mitres, 
and Harps, are worth several times their 
weight in gold; that more than a hundred 
pounds have been paid for a Chinese wentle- 
trap, and that the Cyprea aurora, which the 
Polynesian chiefs used to wear about the neck, 
is valued at thirty or forty guineas. 
The mode in which these beautifully painted 
in structures are formed is very similar to what 
Orange Cone-Shell._ takes place among bivalve shells. They are 
secreted by the glandular margin of the mantle or soft 
skin which clothes the upper part of the body of the snail, 
= Harp-shell. 
Mitre-Shells. 
and their form depends on the shape of the body they 
are destined to cover, while the outline of the border is alike 
regulated by that of the mantle. In the border of the mantle 
