enlarged in most cases so that their distinguishing marks can be seen.
The upright line by the side of each figure gives its actual height.
The shells as numbered are _Helix rupestris_, _H. pygmæa_, _H.
pulchella_, _H. lapicida_, _H. obvoluta_, _H. terrestris_, _H.
barbara_, _Ena montana_, _Ena obscura_, _Pupa secale_, _P. anglica_,
_P. cylindracea_, _P. muscorum_, _Vertigo antivertigo_, _V.
moulinsiana_, _V. pygmæa_, _V. alpestris_, _V. substriata_, _V.
pusilla_, _V. angustior_, _V. edentula_, and _V. minutissima_. Without
a magnifying glass it will be seen that it would be very hard to
distinguish some of the minute shells, but this enlargement enables us
to see the characteristic denticles in the mouth, and the presence or
absence of striations on the shell.
[Illustration: Some of our smaller shells. Actual size indicated by
the upright line.]
_Pupa (Abida) secale_ is named from the Latin for rye, a grain of
which the shell more or less resembles. Conical, brown, mouth
horseshoe-shaped with eight white denticles. Our largest Pupa. Local,
but abundant where found. Prefers calcareous rocks or woods.
_Pupa (Lauria) anglica._--Small, ovate, purplish in colour; mouth like
that of _secale_. Lives in moss, mainly in the north of Britain.
_Pupa (Lauria) cylindracea._--Small, cylindrical, paler than the last;
thick and reflected white lip with one denticle. Abundant. On stones,
in moss, under leaves and bark.
_Pupa (Jaminia) muscorum._--Common, especially on sandy soils near the
sea. Mouth nearly circular, whereas in the two former species it is
horseshoe-shaped. The lip is thin and not reflected.
The genus Vertigo (_i.e._ twisted, the Latin equivalent of the Greek
Helix) contains shells even smaller than the Pupæ, about the size of a
pin's head.
_Vertigo (Alæa) antivertigo_ (_i.e._ not reversed or sinistral, as are
_V. pusilla_ and _V. angustior_). Semi-transparent, glossy,
horn-colour, with denticles (as have all except _V. edentula_ and _V.
minutissima_). Found in nearly all counties in moist places.
_Vertigo (Alæa) moulinsiana._--Our largest species, though only 2-1/3
millimetres in height. Mainly in marshy places. Not common.
_Vertigo (Alæa) alpestris._--Rare and local, chiefly northern. Nearly
transparent shell.
_Vertigo (Alæa) pygmæa._--Common, and often in colonies at roots of
grass and under stones and logs. Not confined to moist places.
_Vertigo (Alæa) substriata._--Local. Strongly striated.
_Vertigo (Vertilla) pusilla._--Sinistral, as is also
_Vertigo (Vertilla) angustior._--Both species rare and local. The
former is the larger and broader. In the former the last whorl is
broadest, in the latter the penultimate. In the former the mouth is
semi-oval, in the latter triangular. In the former the outer lip is
very slightly, in the latter very deeply contracted. The former has 6
to 7 teeth, the latter 4 to 5.
_Vertigo (Sphyradium) edentula_ is dextral and without denticles.
Perhaps the most common _Vertigo_. Partial to bracken.
_Vertigo (Isthmia) minutissima._--Dextral and without denticles.
Smaller, narrower, and more strongly striated than edentula, but
rarer. All the Pupæ should be examined with a magnifier.
_Balea perversa_ (_i.e._ sinistral) is a much larger shell belonging
to the Clausilia family. Thin, dark horn-colour, semi-transparent,
glossy, 7 to 8 whorls, local, but abundant where found. Chiefly found
on trees.
_Clausilia (Pirostoma) bidentata._--All our British clausilias are
sinistral. The clausilium (little door) is an internal contrivance
fastened to the pillar of the shell (whereas an operculum is attached
to the body of a mollusc) by an elastic ligament to protect it against
insect enemies when the animal withdraws. _Bidentata_ has two
denticles, fusiform and reddish-brown, as are all. Very common on
walls and trees.
_Clausilia (Pirostoma) rolphii._--Rare and local. Almost subterranean
in habit. More coarsely striated than the last. The upper whorls
nearly of the same breadth, forming a short cylinder.
_Clausilia (Alinda) biplicata._--Very local. Chiefly on Thames
willows. Larger than the two former, and streaked with white.
_Clausilia (Marpessa) laminata._--Much like the former, but widely
distributed. Usually found on beech and ash trees, and on limestone
rocks. Smooth and glossy.
In the family Stenogyra we have three genera, Azeca, Cochlicopa, and
Cæcilioides (with also the imported _Stenogyra Goodallii_, found only
in pine-houses).
_Stenogyra (Azeca) tridens_ is a small chrysalis-shaped, solid but
semi-transparent shell, horn-coloured, with 3 denticles. Not rare in
moist places.
_Stenogyra (Cochlicopa) lubrica_ (_i.e._ slippery).--Very common in
moss and under stones or logs. Much like the previous species, but no
denticles and fewer whorls, and broader mouth.
_Stenogyra (Cæcilioides) acicula._--If this word is supposed to be
Latin it would mean either "like to a blind worm" or "like to a
lettuce"! _Cæcus_, however, being Latin for blind, the allusion is no
doubt to the fact that this wholly subterranean species is eyeless.
The only British representative of a large family of carnivorous
molluscs. I have found it on Saxon bones when unearthed, and in
crevices of limestone underground, but it is generally found dead
amongst the rejectamenta on the banks of rivers. It is a pretty,
glossy white shell, 5 millimetres in height by 1 in breadth.
I may notice here two other land shells, although they scientifically
are grouped amongst the fluviatile Gasteropoda.
_Cyclostoma (Pomatias) elegans._--Common on calcareous soils,
especially chalk. A spiral shell of 4-1/2 whorls, suture very deep.
Mouth circular (whence its name) and provided with a thick shelly
operculum which closes the orifice when the animal retires by means of
an elastic ligament. This and the next species are our only land
shells provided with an operculum, and this shows their derivation
from the marine Gasteropoda (_e.g._ whelk and winkle). Perhaps all
shells were originally marine, but some became first amphibious and
then terrestrial. It is quite unlike any other of our land shells.
_Acicula lineata_ is a very small shell, the size of the Pupæ; mainly
northern in distribution. Feeds on liverworts and fungi. Very local; 6
or 7 whorls. Mouth pear-shaped, with a horny operculum.
The Family Succinea really ranks with the land shells, as belonging to
the sub-order Pulmonata or lung-breathing molluscs. It is, however,
amphibious, and hibernates in the mud at the bottom of a ditch.
_Succinea putris_ (it is the mud, not the animal, which is putrid!) is
called the Amber Snail from the colour of its shell, which is unlike
any other. Common on flags, etc., at the edges of ditches and ponds.
_Succinea elegans._--Difficult to distinguish from the former, but the
animal is darker and the shell more slender, with a deeper suture and
a narrower mouth.
_Succinea oblonga_ is local and rare. Generally found near the sea.
Much smaller than the other Succineas, and easily mistaken for the
young of other species. Colour dull greenish.
The family Auriculidæ is represented in Britain only by _Carychium
minimum_; a very small, semi-transparent, white and glossy shell found
under mossy stones and other moist places. Common, but sharp eyes are
needed to find it.
* * * * *
We now come to the freshwater shells, which we capture best by means
of a perforated scoop, whether they are on the waterweeds or hidden in
the sand or mud of the bottom.
It may be noted that all freshwater shells are greenish-brown which is
an excellent protective colouring as rendering them less visible among
water weeds to the fish, which devour them greedily.
The family of Limnæidæ (or lake dwellers) has the sub-families,
Planorbis, Physa, Limnæa, and Ancylus. In the Planorbinæ (_i.e._
flat-coiled) the only representative of the genus Segmentina is
_Segmentina nitida_, a small, quoit-shaped, keeled, semi-transparent,
light brown shell, with internal divisions like those of a nautilus
which are visible from the outside of the shell. Local. Found in
stagnant or sluggish water. The genus Planorbis contains the
sub-genera Hippeutis, Gyraulus, Gyrorbis, Coretus, and Bathyomphalus.
_Planorbis (Hippeutis) fontanus_ is much like Segmentina but has no
septa, and is flatter. Common, especially on watercress. Often
encrusted with mud.
_Planorbis (Gyraulus) nautileus_ is very small; quoit-shaped, with the
upper side flat. Grey and striated. The variety crista has the ridges
of the epidermis drawn into points, and is beautiful when seen by a
magnifying glass. Common in ponds and ditches.
_Planorbis (Gyraulus) dilatatus_ is a very small shell imported in
cotton bales from America, and naturalized in canals in Lancashire. No
other of its kind is so small.
_Planorbis (Gyraulus) albus_ is dull white and striated. Flattish
above, with spire depressed. Frequently encrusted and black with mud.
Common.
_Planorbis (Gyraulus) parvus_ (but not so small as
_dilatatus_).--Convex above with a central depression, concave
beneath. Suture deep, and umbilicus large. Smooth and glossy. Local.
_Planorbis (Gyrorbis) spirorbis._--Very flat, glossy, brown, whorls 5
to 6. Common in ponds and ditches.
_Planorbis (Gyrorbis) vertex._--Very like the last, but flatter and
thinner, and with a prominent keel. More local than _spirorbis_, but
sometimes found with it. Whorls 6 to 8.
_Planorbis (Gyrorbis) carinatus._--Larger than _spirorbis_ and
_vertex_. Sharply keeled in the centre of the outer margin. Mouth
angulated above and below. Local, mainly in the south and east of
England.
_Planorbis (Gyrorbis) umbilicatus._--Like the last, but the keel is
below and not on the centre. Mouth rhomboidal. More common than
_carinatus_.
_Planorbis (Coretus) corneus._--Far the largest species. Dark brown,
lighter below. Mouth nearly circular. Spire sunk. In boiling water
often exudes a crimson fluid. Common.
_Planorbis (Bathyomphalus) contortus._--Small, 8-whorled, flat above,
very convex below. Fairly common in still water. Very compact in
appearance.
The sub-family Physa has two genera, Aplecta and Physa.
_Physa (Aplecta) hypnorum_ is a spindle-shaped, very glossy,
semi-transparent, dark reddish brown, shell, with 6 to 7 whorls. Not
common. Found in still water.
_Physa (Physa) fontinalis._--More common, and found in running as well
as in still water. Shorter and more rounded than the last. Shell very
thin, greenish horn-colour. Lobes of the mantle expand over the shell.
Seen in an aquarium are its perpendicular threads of mucus, up and
down which the animals climb.
_Limnæa (Amphipeplea) glutinosa._--Very local. Somewhat like _Ph.
fontinalis_, but larger and more thin. In young specimens the mantle
covers the shell, and in adults the animal is not wholly contained in
the shell.
_Limnæa (sub-genus Radix) involuta._--Only found in one Irish tarn.
Whorls envelop the spire. Very thin, pale amber.
_Limnæa (Radix) peregra._--The most common and variable of all our
freshwater shells. Spire pointed. Somewhat amphibious. Found
practically over the whole of the Eastern Hemisphere.
_Limnæa (Radix) auricularia._--Mouth very large, with outer lip widely
reflected. Very common and fine in the Thames. Spire very short, apex
sharp.
_Limnæa (sub-genus Limnophysa) stagnalis._--The largest of the genus.
Common, except in Wales. Shell greyish, spire long and tapering to a
point; 12210 teeth on its lingual ribbon. See the illustration on p.
57, which also shows above two specimens of _Paludina contecta_, one
being covered (as freshwater shells often are) by a vegetable growth,
which obscures the marking.
_Limnæa (Limnophysa) palustris._--Shell tapering, somewhat solid,
brown, much smaller than stagnalis. Common in slow or stagnant water.
Some varieties much darker than the type.
_Limnæa (Limnophysa) truncatula._--Like the last in shape, but much
smaller, and with a deeper suture. Common, and fond of being out of
the water. A parasite of this mollusc causes "fluke" in sheep which
have taken it in by drinking or by eating grass by the side of ponds
and ditches.
[Illustration: _Paludina contecta_ (two) and _Limnæa stagnalis_ on
water-weeds.]
_Limnæa (Omphiscola) glabra._--Also amphibious. About the same size as
_truncatula_. Local. Inner lip rather thick and reflected on the base
of the penultimate whorl.
_Limnæa (Ancylus) fluviatilis._--"Freshwater limpet." Shell, rather
limpet-like, with a hooked apex (whence its generic name), adheres to
stones or piles in running water. Common. I once dredged a large
water-beetle with three of these shells adhering to its wing-cases;
thus it would be transported to fresh habitats.
_Limnæa (Acroloxus) lacustris._--Like the former but more local, and
preferring sluggish or still waters. Shell more oblong, thinner, and
apex twisted to the left instead of to the right as in _fluviatilis_.
The sub-order Pectinibranchiata (comb-like gill) contains the genera
Neritina, Paludina, and Valvata, in all of which there are two
tentacles with eye at the base, and an operculum to the shell.
_Neritina fluviatilis._--Solid, glossy, chequered brown, white, and
purple (but also a lemon-coloured variety). Operculum semi-lunar,
orange, with a projection which serves as a lock to keep the operculum
in position. Not rare in England; on stones in running water. See
illustration below, which also shows above _L. (Ancylus)
fluviatilis_.
_Paludina (Vivipara) contecta._--Shell dark green with darker bands.
Conical. Suture very deep. Operculum horny. Viviparous. Local.
_Paludina (Vivipara) vivipara._--More common than contecta. Shell more
oval, not so glossy, light greenish yellow, suture not so deep, no
umbilicus, apex blunt.
[Illustration: _Neritina_ and _Ancylus_.]
_Paludina (Bythinia) tentaculata._--(The eyes in this genus are not on
foot-stalks; the operculum is shelly instead of horny). Common in slow
water and ditches. Shell semi-transparent, yellowish, mouth oval,
angulated above. Operculum made of plates rising one above another
formed at different stages of growth.
_Paludina (Bythinia) leachii._--Much smaller and less common than the
last. Distinct umbilicus; mouth almost circular.
_Paludina (Paludestrina) ventrosa._--A brackish-water shell, swarming
where found, _e.g._ from Erith to Gravesend, and in East Anglia. Shell
small, thin, semi-transparent.
_Paludina (Paludestrina) jenkinsi._--A larger shell, not confined to
brackish water and spreading very rapidly. Swarms where found. A
variety has a marked keel which sometimes bears bunches of spines at
equal distances.
_Paludina (Paludestrina) stagnalis._--Larger and with more whorls. Not
so common.
_Paludina (Pseudamnicola) anatina._--Small, sub-conical, deep suture.
Found in brackish water, and apparently identical with _Hydrobia_ or
_Paludestrina similis_, which I used to find by the Thames, where it
is now apparently extinct.
_Valvata piscinalis._--Globular, suture very deep, circular mouth,
operculum concentrically spiral. In ponds and slow water. Shell
yellowish, but commonly covered with conferva.
_Valvata cristata._--Much smaller; shell disk-shaped. Frequents the
roots of flags. Shell striated and more or less ridged, but the name
_cristata_ refers to the plume-like appearance of its breathing
apparatus.
* * * * *
We now come to the bivalve shells with leaf-like gills. The Unionidæ
contain two genera, Unio and Anodonta, commonly called freshwater
mussels.
_Unio tumidus._--Shell ovate, very solid, dark brown; common. See
accompanying illustration, which shows the fringed branchial siphon
which draws in food-bearing water, and the smaller anal siphon by
which it gets rid of undigested matter.
[Illustration: Freshwater mussel breathing and eating.]
_Unio pictorum._--More oblong and thinner shell, yellowish, girdled
with brown in the lines of growth. Common. The specific name recalls
that gold and silver paint used to be sold in these shells (or marine
mussels) for illuminating work. It is said to produce 220,000 eggs in
the three summer months.
_Unio (margaritana) margaritifer._--Shell solid and black, beaks
always eroded. Mainly found in mountain streams. Its pearls are few
and poor compared with those of marine shells; but they attracted the
notice of Cæsar and so hastened the conquest (and development) of
Britain.
_Anodonta cygnea._--(In this genus the hinge is toothless, whence its
generic name. The specific names _cygnea_ and _anatina_ mean "swan"
and "duck," in reference to their comparative size). This is the
largest of our freshwater shells, reaching even 9 inches in breadth by
4-1/2 in length. Common in ponds and slow water. Sometimes the shells
are yellowish green with rays of the same colour.
_Anodonta anatina._--Doubtful if this is a separate species or only a
smaller form. The hinge line is raised instead of being straight, and
the posterior side slopes abruptly instead of gradually.
In the next family are two genera, Sphærium and Pisidium.
_Sphærium corneum._--Very common. Shell somewhat globular, glossy,
opaque, horn-coloured, marked with lighter bands in the line of
growth. Usually on the bottom, but can suspend itself by threads of
mucus.
_Sphærium rivicola._--Much larger. Also flatter and more striated.
Yellowish brown or greenish. A whole series of young of different
sizes will be found in the animal.
_Sphærium pallidum._--Local in canals and ponds. Oblong.
Distinguished also from the previous species by the body being
milk-white, and the shell is ashy-grey.
_Sphærium lacustre._--Local. On the beaks is a calcareous nucleus
which distinguishes it. It is thinner than _corneum_, and rounder than
_pallidum_.
_Pisidium amnicum._--(Our five _pisidia_ resemble _Sphærium_, but are
much smaller, all but _amnicus_ being minute. Very abundant where
found. _P. amnicum_ and _fortinale_ are triangular in shape, _P.
pusillum_ oval, _P. nitidum_ round, and _P. roseum_ or _milium_
oblong; but they are difficult to distinguish on account of their
similarity and variation). _P. amnicum_ is nearly twice the size of
the others, and this and _fontinale_ may be found in slow rivers,
whereas the others prefer stagnant waters.
_Pisidium fontinale._--Smaller and thinner, and with more prominent
beaks than _P. amnicum_.
_Pisidium pusillum._--The most common species. Distinguished from the
last by being oval and by its beaks being blunter and more central.
_Pisidium nitidum._--Rare. Very glossy and striated.
_Pisidium roseum_ (from the colour of part of its body).--Like
_nitidum_, but oblong, with a straight lower margin, and with beaks
placed away from the centre.
The last shell to be mentioned could not be mistaken for any other. It
belongs to the sub-order _Heteromya_ (_i.e._ with adductor or closing
muscles not equal); to the family of _Mytilidæ_ (or mussels) and the
genus _Dreissensia_ (named after a Dutch conchologist).
_Dreissensia polymorpha_ is a triangular, boat-shaped, bivalve,
supposed to have been introduced with Russian timber (as was also
probably _Hydrobia Jenkinsi_). It is gregarious, and attaches itself
to objects by a byssus like our marine mussels. Shell yellowish-brown
with wavy purplish lines, wrinkled in the line of growth. Common in
the New River, and has been found in iron water-pipes in Oxford
Street.
* * * * *
All our shells have varieties (many an albino or white form), and the
collection and distinguishing of these varieties, which in some
species are numerous, adds much to the interest of the collector. In
addition there are also the variations in size or markings which can
hardly rank as varieties. Inasmuch as none of our shells are peculiar
to our country (which is from the natural history and the geological
point of view only a detached portion of the Continent), it may be
well to warn young collectors that if they receive shells from the
Continent, mere varieties are there often named as separate species
and variations considered as definite varieties. This is especially
the case with _Helicella virgata_.
As to the arrangement of shells in a collection before a regular
cabinet is obtained, the tinier shells may be kept in small glass
tubes with corks (such as used for homoeopathic medicines), and the
medium sized ones in the trays of common matchboxes, these being
arranged in large shallow glass-covered trays which can be obtained
from any cardboard boxmaker at a small cost, and several of these,
stored one above the other, form an excellent substitute for a more
costly cabinet. In all cases the name, and the place where the shells
were found, should be written on a small slip of card placed in the
tube or tray. It is not well in most cases to fasten the shells on
card, but if this is done gum tragacanth is best. The collection
should be kept free from damp and from dust.
HINTS FOR COLLECTING AND PRESERVING SHELLS OF MOLLUSCS.
The following notes supply a few general rules as to finding and
preserving shells:--
Of Shell-bearing Molluscs there are three classes--Marine, Freshwater,
and Land. The first two include Univalves and Bivalves, the last only
Univalves.
1. MARINE SHELLS may be obtained, 1st, by searching on and under rocks
at low water, or on coral reefs, among seaweed attached to them, or
floating on the sea, or on a sandy beach. Bivalves may be found by
digging in the sand, or mud, on a beach, or at the mouth of a river:
their presence is generally indicated by a circular breathing hole in
the sand. 2nd. By dredging, by which means only deep-sea shells can be
obtained; but after a storm these may often be found upon the shore,
before they have lost their lustre.
Limpets, etc., should be detached with a thin blade passed quickly
under the shell, taking care not to break the edges. Small shells on
and in seaweed, and limpets, etc., adhering to stones will drop off
and sink to the bottom in a vessel of cold fresh water.
2. FRESH-WATER SHELLS may be obtained in any river, lake, pond, marsh
or reservoir. Univalves, chiefly on the banks, on reeds and plants
growing near the hedges, and on the under surface, leaves, and stems
of aquatic plants. Bivalves generally at the bottom, among stones, or
buried in the sand, or among the roots of aquatic plants.
3. LAND SHELLS.--These resemble, more or less, in their habits the
garden snail, though varying greatly in character, size, and colour.
They mostly abound in a chalk or limestone district, and in moist and
wooded situations. Some species inhabit low and damp spots, roots of
trees, hollows and crevices of rocks and walls; some lie under stones
or pieces of wood, or in the earth; others climb shrubs, and in
tropical climates even lofty trees. Their haunts vary according to the
weather and the season. They come out early in the morning, and after
rain. Some bury themselves in moist places during the dry season, or
burrow under leaves, grass, or stones, often closing the mouths of
their shells with a white secretion to prevent evaporation during the
period of hibernation.
The smallest shells, especially of land species, and young imperfect
shells should be collected.
In all cases "live shells," _i.e._ shells in which the animal is
alive, are to be chosen; but, when these cannot be procured, "dead
shells," which have not lost their lustre, or their colour, especially
those of rare species, should be preserved.
_With regard to the mode of Preserving Shells._
1. No attempt should be made to clean them, or to remove the furry
skin, more or less thick, with which they are often covered, beyond
removing with a soft brush any mud or sand adhering to them.
2. The animals of Land and Freshwater shells may be killed by
immersing them for a few minutes in _boiling_ water, after which the
bodies may be easily extracted whole with any suitable instrument,
_e.g._, a fork or a pin, according to size. Hot water should not be
used with marine shells: it often destroys their lustre. They should
be buried, if time permits, in sand, or other dry material, until the
animal dries up (in small shells) or rots (in large specimens); or
they may be drowned in cold fresh water, and hung up in the air to dry
or rot away. In the former case, if an operculum (with which some
species, both marine and land, close their mouths, more or less
partially) exists, it will, generally in the case of land shells,
remain in its place, adhering to the shell. In the latter, the decayed
matter should be washed out, and the operculum, if any, replaced and
fixed, say, on cotton filling the shell. This applies equally to land
shells.