174 PECTINIBRANCHIATA.—MURICID&. | 
organs can be folded within the narrow compass of 
the shell, and protruded through so contracted an 
aperture. 
Famity Muricipaé. 
(Whelks, &c.) 
The Rock-shells and the Whelks, with their 
numerous allies, have commonly been considered 
as constituting two families, the Muricide and the 
Buccinide, or, to use the terms of Professor De 
. Blainville, the Stphonostomata and the Entomosto- 
mata. But by Messrs. Forbes and Hanley all 
these mollusca are united in one family, under the 
name first mentioned ; and this appears to be their 
true relation to each other; for even De Blainville 
confesses that his two families differ evidently very 
little, whether in the soft parts or the shell. 
The species which, thus united, are very nu- 
merous, have the following characters in common : 
The shell is very variable in form, but always dis- 
tinctly spiral, often turreted, with an aperture vary- 
ing im size from excessive width to excessive 
narrowness, but always provided with a canal, 
which is sometimes produced into a long gutter, at 
others is contracted to a mere notch. 
The animals are distinguished by a spiral body, 
with the foot, which is shorter than the shell, 
rounded in front. The mantle is furnished in front 
of the breathing-chamber with a long canal, 
always uncovered, which is used as an organ of 
prehension. ‘I'he head is crescent-shaped, with a 
protrusile, proboscis-like mouth, whence is unfolded 
a ribbon-shaped tongue, armed with teeth arranged 
in triple rows, of three in arow. ‘The breathing 
