Chapter II: Part 2

_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.

_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.

_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.

_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.

3. Care should be taken not to injure the edge or lip of the mouth of univalves, or the ligament of the hinge of bivalves. When bivalves gape on dying in water, or if the ligament be broken, the valves should be closed and tied together. If the ligament of a gaping bivalve should become dry and stiff, it can be softened by putting it in water.

4. The localities in which each species is found should be noted, and, in the case of dredging, the depth of water.

_With regard to the mode of packing Shells for Transport._

All solid shells may be wrapped in one or two folds of paper of any kind. Fragile and minute shells should be put, generally separately, into a box or bottle--with or without cotton, as required. Such packets may be heaped up in any box, heavy shells at the bottom, without pressure, and any blank filled at the top with paper or other elastic material. Sawdust injures the lustre of many species.

Two books on shells should be procured at an early stage of the collector's career, which will give not only minute descriptions of all our land and freshwater shells and their varieties, but also plates of illustrations. These are the _Collector's Manual_, by L. E. Adams, 2nd ed., published by Taylor Brothers of Leeds; and Rimmers' _Land and Fresh Water Shells_, published by George Grant of Edinburgh.

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