[Sidenote: NERITACEA. NERITINA.]
"The family of the _Neritacea_," said Mr. Elliot, as he renewed his
lessons to Charles and Lucy, "are remarkable in their form. Their
left-margin is truncated, without any appearance of a columella. They
possess an operculum, and are either marine or fluviatic. The genera
are,
_Navicella._
_Neritìna_ _Nerìta_, Nerite, or hoof-shell.
_Nerìta_ _Nerìta_.
_Natìca_ _Nerìta_.
"You will recollect that the order _Trachelipoda_ is still continued.
"_Navicella_ is a foreign genus from the Indian rivers.
[Sidenote: NERITINA. NERITA.]
"_Neritìna_ is a pretty genus of shells, from the European, the East
and West Indian rivers. They resemble the _Nerìta_ genus, but are all
fresh-water shells; thin, smooth, and variously marked; without any
tooth or notch on the right-margin of the aperture.
"_N. virginea_ is common in collections; it is marked with various
lines and dots.
"_N. fluviatilis_ is common in our rivers: you may find plenty in
river-sand, of red and brown colours, and various sizes.
"_N. zebra_ and _N. meleagris_ are also pretty shells. The little
_Neritìna viridis_, from the West Indian streams, is one of the
smallest species, of a pale pellucid green.
"_Nerìta_ is a marine genus. The shells are solid and semi-globose; the
left-margin is truncated, the right-margin toothed, or crenulated. This
genus is never umbilicated.
"_N. polìta_ is a handsome shell: it is thick, polished, and variously
marked; the base of the aperture is yellowish.
"_N. peloronta_, the bleeding-Nerite, is marked with a crimson spot.
"_N. tessellata_ is sulcated, or furrowed, chequered with black and
white.
"_Natìca_ differs from the former genera in these particulars: the
shell is umbilicated; the left-margin oblique, not toothed, callous,
the callosity sometimes covering the umbilicus. The species are
numerous, and several are common in collections. "_N. aurantius_ and
_N. millepunctata_ are good shells.
[Sidenote: IANTHINA. SIGARETUS. STOMATELLA.]
"_Ianthina_ is the last of the snail-like genera. Its beautiful purple
colour renders the shell a favourite. They are marine, though so
fragile and transparent. The animal floats upon the surface of the
sea, by means of a vesicular appendage to the foot, which, it is
said, may be inflated or contracted at pleasure. _Ianthina_ shines by
night. _I. communis_ is found in abundance in the Atlantic and in the
Mediterranean.
* * * * *
"The family _Macrostoma_ contains,
_Sigaretus_ _Helix_?
_Stomatella._
_Stomatia._
_Haliòtis_ _Haliòtis_, sea-ear.
"These genera form a beautiful family, and all bear a resemblance to
the human ear.
"_Sigaretus_ is white and pearly; the shell is enveloped in the folds
of the mantle belonging to the animal. There are several species, one
or two of which were ranked among the _Helix_ race.
"_Stomatella_ is also very pretty; the shells are pearly. _S.
auricula_, from New Holland, has the appearance of a little _Haliòtis_.
"_Stomatia_ is a small genus.
[Sidenote: HALIOTIS. VERMETUS. SCALARIA.]
"With the genus _Haliòtis_ you are already acquainted. The animal
appears to be very elegantly formed, if the plate I have seen of it be
correct.
"There is a number of fine specimens in the British Museum.
* * * * *
"The family _Plicacea_ contains only,
_Tornatella_ _Voluta_, chiefly.
_Pyramidella._
"All the species have plaits, or folds, on the columella. The shells
are marine and foreign in both genera. (Plate 9.)
* * * * *
"Our next family, _Scalariana_, contains the genera
_Vermetus._
_Scalaria_ _Turbo_.
_Delphinula_ _Turbo_.
* * * * *
"The single species of the first genus, _Vermetus lumbricalis_,
inhabits the sea near to Senegal. The shell is tubular, thin, twisted
spirally; it is fixed on marine substances by the end of its thin,
pointed spire. The shells are usually found in groups.
"The genus _Scalaria_ is one of the most elegant among univalve shells.
The singularity of the numerous ribs renders the shells easily known
from all other genera of turreted _Mollusca_. The aperture is nearly
round, the whorls gibbous, or inflated with carinated ribs: the colour
is usually pink or white. It is very costly. (Plate 9.) These
shells are brought from the East Indies.
"The fossil species are very elegant: they are found in the strata
above the chalk.
"Two other species are common, _S. communis_ and _S. lamellosa_. The
first is a British species, and is called the _false Wentletrap_.
[Sidenote: DELPHINULA. SOLARIUM.]
"The shells of the genus _Delphinula_ are solid, thick, somewhat
discoid, often armed with spines, without any apparent columella. The
recent species inhabit the Indian Ocean. There are several fossil
species of _Delphinula_.
"The _Turbinacea_ family contains many genera, with which you will soon
become familiar. I believe you are already acquainted with this shell,
which, from the time it was first known to collectors, has always
been celebrated for beauty. It is now called _Solarium perspectivum_.
(Plate 9.) The large, spiral, crenated umbilicus is its great
peculiarity. The French call the shell _Cadran_, _dial_. In its natural
state the shell is covered with an epidermis. There are a few fossil
species, one in the oölite of our own country. The English name is
_staircase trochus_.
* * * * *
[Sidenote: ROTELLA. TROCHUS. TURBO.]
"The genera of _Turbinacea_ are,
_Solarium_ _Trochus_.
_Rotella_ _Trochus_--wheel-shell.
_Trochus_ _Trochus_--top shell.
_Monodonta._
_Turbo_ _Turbo_.
_Planaxis_ _Buccinum_.
_Phasianella_ _Turbo_.
_Turritella_ _Turbo_.
"The genus _Rotella_ contains small, flattened, wheel-shaped shells,
common in most collections. They are smooth and polished.
"_Trochus_ is still a large genus. _Trochus marmoràtus_ is a fine
species from the Indian Ocean. There are several handsome species
on our own shores. _T. magus_ is one of them; it has a large, deep
umbilicus, or perforation; the spire is flattened; the whorls are
crowned with tubercles. The _Trochi_ of tropical climates are thinner
than those of northern latitudes.
"When any of these shells are placed upon their _base_, their axis is
always inclined: of course they never stand perfectly upright.
"There are several fossil species.
"The genus _Monodonta_ holds a middle place between _Trochus_ and
_Turbo_, differing from the former in the aperture, and from the latter
in the columella, which is arched and truncated at the base. They are
all marine shells.
[Sidenote: LITORINA. TURBO. PHASIANELLA.]
"From the well-known genus _Turbo_, a new one has been formed, called
_Litorina_, which includes all the shells of our own coasts that
formerly ranked under _Turbo_. Consequently we find the periwincle
has changed its generic name, and from _Turbo_ it is altered into
_Litorina_. _T. muricata_ is now of the same new genus, _Litorina
muricata_. (Plate 7.)
"_Turbo pica_ is a large pearly shell known as the magpie. The
golden-mouthed _Turbo_ is very brilliant; the aperture appears as if
gilded, so fine is the yellow tint. It comes from the Molucca Isles.
_Turbo smaragdus_, from New Zealand, is a rare and beautiful species of
a bright green colour.
"_Phasianella_ is a beautiful genus of shells, formerly very costly.
A small but elegant species is found on our own shores, _P. pullus_,
_Turbo pullus_ of some authors. The colour is pink.
"_Phasianella bulimoides_, from New Holland, is the largest of the
species, and once a very rare shell.
"The term _Turritella_ will give you an idea of the form of our
last genus in the family _Turbinacea_. The shells are like _little
towers_, with a circular aperture. The older conchologists gave the
name of _screw_ to all turreted shells, without attending to the form
of the aperture. Hence we find screws among _Turbo_, _Buccinum_, and
_Strombus_ (spindle).
[Sidenote: TURRITELLA.]
"_Turritella duplicata_ is a heavy shell, often more than four inches
long. It is sulcated and carinated; the colour is yellow-white. _T.
bicingulata_ is white, marbled with yellow; the whorls are girded with
two ridges. There are several fossil species of this genus in London
clay."
"I think," said Lucy, "that three or four genera have been taken out of
_Turbo_--_Scalaria_, _Delphinula_, _Litoralia_, and _Turritella_, and
that _Litoralia_ is not Lamarck's genus."
"You are correct," replied her father, "and indeed so many alterations
are continually taking place in the generic names of shells, that I
cannot enter into all the niceties of modern conchologists. However,
the generic name of a shell, according to Linnæus or Lamarck, is
usually given, therefore I hope you will not be greatly at a loss upon
meeting with some apparently unknown genus."