112 
NATURAL HISTORY. 
[east. ZOOL. 
mal to be very different from that of the young. This ex¬ 
pansion only takes place once in their lives, and not at re¬ 
peated and stated periods, as in the Murices, &c. Their 
operculum is narrow and claw-like, the apex being pro¬ 
duced beyond the point of its attachment, as it enlarges, 
by new layers below, and the tube of the syphon is al¬ 
ways bent towards the right side. 
All the other flesh-eating comb-gilled Gasteropodes have 
a broad expanded foot, by which they glide on and attach 
themselves to marine bodies; their eyes are sessile, or 
placed on a very short tubercle near the base, or on the 
tentacles. 
The family of Murices ( Muricidce , Case 3) have a more 
or less elongated straight syphon, and the shell has a 
straight tubular canal for its protection ; the animal, at cer¬ 
tain periods of its growth, expands the edge of its mantle, 
and, during this time, deposits appendages on the edge of 
the shell for their protection; these expansions of the man¬ 
tle are then gradually withdrawn, and the portion of shell 
which the animal forms between this time and the next 
developement of the appendages, is of the common shape: 
but the expansions produced for their protection are left on 
the surface of the shell, forming variously shaped bands 
across the whorls, which have been called varices, from 
some of them looking like dilated veins; these varices, 
and the spines upon them, being formed on the expanded 
appendages of the mantle, exactly correspond to them in¬ 
form, and afford good characters for the determination of 
the groups and species. In some of these animals the 
periodical expansions of the mantle are round, forming a 
convex simple granular varix on the shell, and the inner lip 
of the shell is generally granulated; as in the genera 
j Ranella, where there is half a whorl between each varix, 
and Triton , where there is a varix on each two-thirds of a 
whorl. In the Murices, on the contrary, the expansions of 
the mantle are generally produced into elongated processes, 
the varices are consequently spinose or variously branched, 
and there is only one-third (or often less) of a whorl between 
them : the inner lip of these shells is smooth. In the other 
genera of this family the animal does not, or only very 
slightly, dilate the mantle at any period of its growth, so 
that the shell has a uniform surface, or marked with only 
