34 Rev. L. Guilding’s Observations on the Chitonide. 
at leisure. If the existence of the operculum is doubiful, or the animal 
has withdrawn itself from sight, a specimen may be fractured and suf- 
fered to rot m spring water, when the putrid mass must be carefully 
washed and examined in a watch-glass. By these means I have detected 
the spurious operculum in species which I believed possessed it, but in 
which it could not, in the common way, be detected after the most pa- 
tient examination. In Colombella it is sometimes so minute as to require 
a sharp eye, or even a magnifier, before it can be found. In such cases 
itis indeed spurious, or only the rudiment of the organ, which may be 
more perfectly developed in other species, or in kindred genera, which 
from their economy require an ampler shield against the attacks of 
enemies. 
We are apt, however, to make use of this word spurious without suffi- 
cient consideration. We should recollect, when wondering at the small- 
ness or weakness of the horny opercula of some Mollusca, that the spe- 
cies which possess such either live under the sand, reside in safety on the 
coasts, or quit the waters when they are not feeding, the shell being held 
down close to the rocks by a dried mucous secretion, as in some Turb?- 
nide, or by the mere adhesion of the foot, as in Purpura, &c. The 
operculum, which in many cases would not close the expanded aperture, 
is only brought into use in cases of great peril, when the hold of the 
adhesive foot is loosened, the’ vessels are emptied of mucus, the various 
secretions, or the poisonous or coloured fluidsby which the enemy is to be 
driven back or baffled, and the animal retires into the narrower whorls, 
for which alone the operculum is fitted. When the operculum is per- 
fectly solid and testaceous, we may be sure that its possessor commonly 
resides in places where it is subject to the sudden attacks of dangerous 
pursuers. Here it will be of ample size, and capable of closing the 
larger and exterior whorl. The structure and composition of this organ 
indicates the habits of the inhabitant in so many cases, that its value in 
generic characters is far greater than many are willing to allow. 
Before concluding these notes on the Chitonide, I cannot refrain from 
again referring to the complex and wonderful organs of the mouth for com- 
minuting the food. The Palato-cesophagal membrane, when the animal is 
plunged into boiling water, is easily detached, and forms a beautiful and in- 
teresting object for the microscope. The anterior termination is expanded 
