CONCHOLOGY. 
admits there are many intermediate forma- 
tions. The number and form of the spires 
vary in the same species, in their different 
growths. Young shells have commonly a 
less number than the old ones, neither have 
shells of the same age always the like num- 
ber of spires, a circumstance attributable 
to the effects of sickness, or the difference 
of sex. Thus in some turbinated shells we 
perceive that the males have the spires less 
numerous, smaller, and in a more lengthen- 
ed form than in the females. 
Suture of the spire or whorls, is the spi- 
ral line which separates the whorls, and 
which is sometimes sulcated, crenulated, or 
somewhat projecting. 
Pillar or columella, is the inner part of 
tlie left lip or column, which runs through 
the shell, from the lower extremity to the 
tip of tlie spire, and from which all the 
spires take their origin ; the columella be- 
ing situated as nearly as possible in the axis 
of the shell, and serving as its basis and sup- 
port throughout. It is generally either flat, 
grooved, folded, or truncated in that part 
which is visible at the opening. 
Aperture, called in familiar language, the 
mouth of the shell, is the entrance to the 
chamber in which the animal resides, and 
is applicable to the openings of univalve 
and multivalve shells. The aperture is ei- 
ther entirely open, or closed by tlie oper- 
culum attached to the body of the animal, 
when the animat retires into its dwelling. 
This aperture varies in form in different 
shells, being angular, rounded, semilunar, 
linear, or otherwise, and sometimes appears 
double, the inner margin being surrounded 
by an exterior one. 
Lip. The expansion of the exterior part 
of the aperture constitutes the lip in the la- 
biated shells, and the wing in the alated 
kinds. 
Beak, or rostrum, is that part at the base 
which extends in a straight or slightly ob- 
lique direction from the bottom of the aper- 
ture, and is larger or smaller in different fa- 
milies. In the murex haustellum this pro- 
jection is very conspicuous. 
Canal, or gutter, an elongation of the 
aperture of the shell descending in a groove 
or gutter-like process. Some kinds of ro- 
strated shells have the canal remarkably 
conspicuous, forming a sinus from the aper- 
ture throughout the whole length of the 
beak. 
Umbilicus, is the opening or perforation 
in the lower part of the body, or first whorl 
of many spiral univalves, and is very con- 
spicuous in a number of the trochus and ne 
rita genus in particular. This umbilical 
perforation runs in a straight line from toe 
base to the summit -of the shell, forming 
throughout a spiral groove or gutter, which 
is wide at the entrance, and tapers gra- 
dually towards the apex. In the Linnsean 
nerita canrena, the structure of the umbili- 
cus is well displayed, but is still more ob- 
vious in the staircase shell, trochus perspec- 
tivus. This opening occurs in many shells 
at the base of the pillar. 
Operculum is a testaceous or cartilaginous 
appendage peculiar in a considerable de- 
gree to the univalve tribe of shells, and 
those only of the spiral or turbinated kinds. 
This appendage is not connected with the 
shell, but the animal, and serves like a lid 
or little door, to protect or close up the 
aperture of the chamber when the creature 
retires within its habitation. Shells of this 
kind are distinguished by the name of coch- 
leae operculat®, by some of the elder con- 
chologists. The opercula are often small in 
comparison to the size of the shell to which 
they belong ; their form varies in different 
species ; and their substance in some of a 
horny texture, and, in others, testaceous or 
approaching the nature of stone. Their 
figure in common is cither perfectly round, 
elliptical, oval, or elongated, and some- 
times wrought with spiral work, or concen- 
tric lines. 
Epidermis is a kind of skin or coating, 
with which the exterior surfaces of many 
shells, both of the univalve and bivalve 
tribe, are covered. It is considered as a sort 
of periosteum or membrane, designed by 
nature to defend the shell from accidents 
and aid their growth, and to prevent other 
testaceous or marine animals from fixing 
their habitations on these shells, as they do 
upon most bodies in the sea, where there is 
no power of resistance. The epidermis is 
a genuine covering formed by the animal 
itseltj peculiar to some kinds, and as con- 
stantly never observed on others. There is 
no doubt but the animal to which this sort 
of covering is peculiar, possesses a proper 
apparatus for its consti’uction. The struc- 
ture of this epidermis, it should be added, 
is very distinct in different shells, consisting 
in some of a very thin pellucid film, and in 
others laminated, pilous, velvety, fibrous, 
or rugged. Few shells, having a rugose 
surface, are destitute of this external co- 
vering or epidermis. 
Bivalves, or shells of two valves imited 
by means of a cartilage, hinge, connection 
