Chapter II: Part 2

Text size

The first thing required is some method of keeping the different species of shells apart, so that they may not get mixed, or be difficult to find when wanted. The simplest plan of doing this is to collect all the empty chip match-boxes you can find, throw away the cases in which they slide, and keep the trays, trying to get as many of a size as possible. (The ordinary Bryant & May's, or Bell & Black's, are the most useful, and with them the trays of the small Swedish match-boxes, two of which, placed side by side, occupy nearly exactly the same space as one and a half of the larger size, and so fit in with them nicely.) In these trays your shells should be placed, one kind in each tray; but although very convenient for most specimens, they will of course be too small for very many, and so the larger trays must be made. This may easily be done as follows: cut a rectangular piece of cardboard two inches longer one way than the length of the match-tray, and two inches more the other way than twice the width of the match-tray; then with a pencil rule lines one inch from the edges and parallel with them (Fig. 1); next cut out the little squares (_a_ _a_, _a_ _a_) these lines form in the corners of the piece of cardboard, and then with a penknife cut _half_ through the card, exactly on the remaining pencil-lines, and bend up the pieces, which will then form sides for your tray; and by binding it round with a piece of blue paper, you will have one that will look neat, uniform with the others, and yet be just twice their size. If required, you can make in the same way any size, only take care that they are all multiples of one standard size, as loss of space will thereby be avoided when you come to the next process in your cabinet. This is, to get a large box or tray in which to hold your smaller ones.

+---+-----------+---+
|_a_| |_a_|
+---+-----------+---+
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
+---+-----------+---+
|_a_| |_a_|
+---+-----------+---+

The simplest plan is to get some half-dozen cardboard boxes (such as may be obtained for the asking or for a very trifling cost at any draper's), having a depth of from one to two inches (according to the size of your shells); in these your trays may be arranged in columns, and the boxes can be kept one above the other in a cupboard or in a larger box. More boxes and trays can, from time to time, be added as occasion requires, and thus the whole collection may be kept in good working order at a trifling cost. A more durable form of cheap cabinet may be made by collecting the wooden boxes so common in grocers' shops, cleaning them with sand-paper, staining and varnishing them outside, and lining them inside with paper; or, if handy at carpentering, you may make all your boxes, or even a real cabinet, for yourself.

HOW TO COLLECT SHELLS.

Provision being thus made for the comfortable accommodation of your treasures, the next consideration is, how to set about collecting them. Mollusca are to be found all over the globe, from the frozen north to the sun-baked tropics, on the land or in lakes, rivers, or seas--wherever, in fact, they can find the food and other conditions suitable for their growth and development; but the collector who is not also a great traveller, must of course rely for his foreign specimens upon the generosity of friends, or else procure them from dealers. In most districts of our own country, there are, however, to be found large numbers of shells whose variety and beauty will astonish and reward the efforts of any patient seeker. Begin with your own garden,--search in the out-of-the-way, and especially damp, corners; turn over the flower-pots and stones which have lain longest in one place, search amongst the roots of the grass growing under walls, and in the moss round the roots of the trees, and you will be surprised at the number of different shells you may find in a very short space of time. When the resources of the garden have been exhausted, go into the nearest lanes and again search the grass and at the roots of plants, especially the nettles which grow beside ditches and in damp places; hunt amongst the dead leaves in plantations, and literally leave no stone unturned. All the apparatus it is necessary to take on these excursions consists of a few small match or pill-boxes in which to carry home the specimens; a pair of forceps to pick up the smaller ones, or to get them out of cracks; a hooked stick to beat down and pull away the nettles; and, above all, sharp eyes trained to powers of observation. The best time to go out, is just after a warm shower, when all the grass and leaves are still wet, for the land-snails are very fond of moisture, and the shower entices them out of their lurking-places. Where the ground is made of chalk or limestone, they will be found most abundant; for as the snail's shell is composed of layers of animal tissue, strengthened by depositions of calcareous earthy-matter which the creature gets from the plants on which it feeds, and these in their turn obtain from the soil--it naturally follows that the snail prefers to dwell where that article is most abundant, as an hour's hunt on any chalk-down will soon show.

When garden and lanes are both exhausted, you may then turn to the ponds and streams in the neighbourhood, where you will find several new kinds. Some will be crawling up the rushes near the margin of the water, others will be found in the water near the bank, while others may be obtained by pulling on shore pieces of wood and branches that may be floating in the water; but the best are sure to be beyond the reach of arm or stick, and it will be necessary to employ a net, which may be easily made by bending a piece of wire into a circle of about four inches in diameter, and sewing to it a small gauze bag; it may be mounted either on a long bamboo, or, better still, on one of those ingenious Japanese walking-stick fishing-rods. For heavier work, however, such as getting fresh-water mussels and other mollusca from the bottom, you will require a net something like the accompanying figure (Fig. 2), about one foot in diameter. This, when attached to a long rope, may be thrown out some distance and dragged through the water-weeds to the shore, or if made with a square instead of a circular mouth, it may be so weighted that it will sink to the bottom, and be used as a dredge for catching the mussels which live half-buried in the mud. To carry the water-snails home, you will find it necessary to have tin boxes (empty mustard-tins are the best), as match-boxes come to pieces when wetted.

The finest collections of shells, however, are to be made at the sea-side, for the marine mollusca are both more varied in kind and more abundant than the land and fresh-water ones, and quite an extensive collection may be made in the course of an afternoon's ramble along the shore; it is necessary, however, to carefully reject such specimens as are worn by having been rolled by the waves upon the beach, as they are not of any great value in a collection; it is better, in fact, if possible, to go down to the rocks at low water and collect the living specimens. Search well about and under the sea-weeds, and in the rock-pools, and, when boating, throw your dredge-net out and tow it behind, hauling it in occasionally to see what you have caught, and to empty the stones and rubbish out.

At low tide also, look out for rocks with a number of round holes in them, all close together, for in these holes the Pholas (Fig. 22) dwells, having bored a burrow in the solid rock, though _how_ he does it we do not yet quite know.

The Razor-shells and Cockles live in the sand, their presence being indicated by a small round hole; but they bury themselves so fast that you will find it difficult to get at them. Some good specimens, too, of the deeper water forms are sure to be found near the spots where fishermen drag their boats ashore, as they are often thrown away in clearing out the nets; moreover, if you can make friends with any of the said fishermen, they will be able to find and bring you many nice specimens from time to time.

The reason that so much has been said about collecting living specimens, is not only because in them the shell is more likely to be perfect, but also because in its living state the shell is coated with a layer of animal matter, sometimes thin and transparent, at others thick and opaque, called the _periostracum_ (or _epidermis_), which serves to protect the shell from the weather, but which perishes with the animal, so that dead shells which have lain for some time tenantless on the ground, or at the bottom of the water, exposed to the destructive agencies that are constantly at work in nature, have almost invariably lost both their natural polish and their varied hues, and are besides only too often broken as well. Since, however, even a damaged specimen is better than none at all, such should always be kept until a more perfect example can be obtained.

HOW TO PREPARE THE SHELLS FOR THE CABINET.

The question with which we have next to deal is, after collecting a number of living mollusks, how, in the quickest and most painless manner possible, to kill the animals in order to obtain possession of their shells. There is but one way we know of in which this may be accomplished, and that is by placing the creatures in an earthen jar and pouring _boiling_ water on them. With land, or fresh-water snails, the addition of a large spoonful of table-salt is advisable, as it acts upon them chemically, and not only puts them sooner out of pain, but also renders their subsequent extraction far easier. Death by this process is instantaneous, and consequently painless; but to leave snails in cold salt water is to inflict on them the tortures of a lingering death; while for the brutality of gardeners and other thoughtless persons who seek to destroy the poor snail they find eating their plants by crushing it under foot on the gravel path, no words of condemnation are too strong, since it must always be borne in mind that snails have not, like us, _one_ nervous centre, but three, and are far more tenacious of life; hence, unless all the nerves are destroyed at once, a great deal of suffering is entailed on the poor creature; and if merely crushed under foot, the mangled portions _will live for hours_. Hot water has also the advantage of tending to remove the dirt which is almost sure to have gathered on the shells, and so helping to prepare them better for the cabinet. As soon as the water is cool enough, fish out the shells one by one and proceed to extract the dead animals. This, if the mollusk is _univalve_ (_i.e._, whose shell is composed of a single piece), such as an ordinary garden snail, can easily be done by picking them out with a pin; you will find, probably, that some of the smaller ones have shrunk back so far into their shells as to be beyond the reach of a straight pin, so it will be necessary to bend the pin with a pair of pliers, or, if none are at hand, a key will answer the purpose if the pin be put into one of the notches and bent over the edge until sufficiently curved to reach up the shell. You will find it convenient to keep a set of pins bent to different curves, to which you may fit handles by cutting off the heads and sticking them into match stems. It is a good plan to soak some of the smaller snails in clean cold water before killing them, as they swell out with the water, and do not, when dead, retreat so far into their shells. If you have a microscope, and wish to keep the animals till you have time to get the tongues out, drop the bodies into small bottles of methylated spirit and water, when they will keep till required, otherwise they should of course be thrown away at once. The now empty shells should be washed in clean warm water, and, if very dirty, gently scrubbed with a soft nail or tooth brush, and then carefully dried.

In such shells as the Periwinkle, Whelk, etc., whose inhabitants close the entrance of their dwelling with a trap-door, or _operculum_ as it is called, you should be careful to preserve each with its proper shell.

If you are cleaning _bivalves_, or shells composed of two pieces, like the common mussel, you will have to remove the animal with a penknife, and while leaving the inside quite clean, be very careful not to break the ligament which serves as a hinge; then wash as before, and tie them together to prevent their gaping open when dry.

Sometimes the fresh-water or marine shells are so coated over with a vegetable growth that no scrubbing with water alone will remove it, and in these cases a weak solution of caustic soda may be used, but very carefully, since, if too strong a solution be employed, the surface of the shell will be removed with the dirt, and the specimen spoilt. In some shells the periostracum is very thick and coarse, and must be removed before the shell itself can be seen; but it is always well to keep at least one specimen in its rough state as an example. In other shells the periostracum is covered over with very fine, delicate hairs (_Helix sericea_ and _Helix hispida_, Fig. 3), and great care must then be taken not to brush these off.

HOW TO MOUNT THE SHELLS FOR THE CABINET.

When the specimens are thoroughly cleaned, the next process is to sort out the different kinds, placing each description in a different tray, and then to get them ready for mounting, for no collection will look well unless each kind is so arranged that it may be seen to the best advantage, and is also carefully named. Where you have a good number, pick out first the largest specimens of their kind, then the smallest, then a series, as you have room for them, of the most perfect; and finally those which show any peculiarity of structure or marking. Try, too, to get young forms as well as adult, for the young are often very different in appearance from the full-grown shell. Mark on them, especially on such as you have found yourself, the locality they came from, as it is very important to the shell collector to know this, since specimens common enough in one district are often rare in another. Either write the name of the place in ink on a corner of the shell itself, or gum a small label just inside it, or simply number it, and write the name of the place with a corresponding number against it in a book kept for the purpose. Next select a tray large enough to hold all you have of this kind; place a piece of cotton wool at the bottom, and lay your shells upon it. For small shells, however, this method is not suitable, as the cotton wool acts on them like a spring mattress, and they are liable on the least shock to be jerked out of their trays and lost. This difficulty may be met by cutting a piece of cardboard so that it just fits into your tray, and then gumming the shells on to it in rows; but remember that, in this plan of mounting, it is impossible to take the shells up and examine them on all sides as you do the loose ones, and so you must mount a good many, and place them in many different positions, so that they may be seen from as many points of view as possible. The gum used should always have nearly one-sixth of its bulk of pure glycerine added to it; this prevents it from becoming brittle when dry, otherwise your specimens would be liable after a time to break away from the card and get lost. If the shells will not stay in the position you require, wedge them up with little pieces of cork until the gum is dry.

When the shells are mounted, you must try, if you have not already done so, to get the proper names for them; it is as important to be able to call shells by their right names as it is to know people by theirs. The commoner sorts you will be able to name from the figures of them given in text-books, such as those quoted in the list at the end of this little work; but some you will find it very difficult to name, and it will then be necessary to ask friends who have collections to help you, or to take them to some museum and compare them with the named specimens there exhibited. When the right name is discovered, your label must then be written in a very small, neat hand, and gummed to the edge of the tray or on the card if your specimens are mounted. At the top you put the Latin name, ruling a line underneath it, and then, if you like, add the English name; next, put the name of the place and the date at which it was found, thus:--

=====================================
Helix aspersa (Common snail),
-----------------------------
Lane near Hampstead Heath,
July 10th, 1882.
=====================================

A double red ink line ruled at the top and bottom will add a finished appearance to it.

HOW TO CLASSIFY THE SHELLS FOR THE CABINET.

All the foregoing processes, except the naming of your specimens, are more or less mechanical, and are only the means to the end--a properly arranged collection. For, however well a collection may be mounted, it is practically useless if the different shells composing it be not properly classified. By classification is meant the bringing together those kinds that most resemble each other, first of all into large groups having special characteristics in common, and then by subdividing these into other smaller groups, and so on. Thus the animal kingdom is divided, first of all, into _Sub-kingdoms_, then each _Sub-kingdom_ into so many _Classes_ containing those which have further characteristics in common, the _Classes_ into _Orders_, the _Orders_ into _Families_, the _Families_ into _Genera_, and these again into species or kinds.

The Mollusca, or soft-bodied animals, of whose protecting shells your collection consists, form a sub-kingdom, and are subdivided into four classes:--

1. Cephalopoda.
2. Gasteropoda.
3. Pteropoda.
4. Lamellibranchiata (or Conchifera).

And these again into Families, Genera, and Species.

The space at our disposal being limited, it is impossible to do more than furnish some general outlines of the different forms. For further details it will be necessary to refer to one of the larger works, a list of which will be found on the last page.

CLASS I.--The CEPHALOPODA (Head-footed) contains those mollusca that, like the common Octopus, have a number of feet (or arms) set round the mouth, and is divided into those having two gills. (Order I. Dibranchiata); and those with four (Order II. Tetrabranchiata). Order I. is again divided into: (_a._) Those with _eight_ feet like the Argonaut (or Paper-nautilus, Fig. 4), which fable has so long endowed with the power of sailing on the surface of the ocean, (it is even represented in one book as propelling itself through the air!) and the common Octopus. (_b._) Those with _ten_ feet, such as the Loligo (or Squid, Fig. 6), whose delicate internal shell so much resembles a pen in shape; the Cuttle-fish (Sepia, Figs. 5 & 7), whose so-called "bone" (once largely used as an ink eraser) is frequently found on our southern coasts; and the pretty little _Spirula_ (Fig. 8).

The only representative of the four-gilled order now living is the well-known Pearly Nautilus; but in former times the Tetrabranchiata were extremely numerous, especially the _Ammonites_.

CLASS II.--GASTEROPODA (Belly-footed) comprises those mollusca which, like the common snail, creep on the under-surface of the body, and with one exception (_Chiton_, Fig. 20) their shells are univalve (_i.e._, composed of one piece). But before we go further, it may be well to point out the names given to different parts of a univalve shell. The aperture whence the animal issues is called the _mouth_, and its outer edge the _lip_; each turn of the shell is a _whorl_; the last and biggest, the _body-whorl_, the whorls, from the point at the top, or _apex_, down to the mouth form the _spire_; and the line where the whorls join each other is called the _suture_. The axis of the shell around which the whorls are coiled is sometimes open or hollow, and the shell is then said to be _umbilicated_ (as in Fig. 3_b_); when closely coiled, a pillar of shell, or _columella_, is left (as in Fig. 9). Sometimes the corner of the mouth farthest from the spire and next the columella, is produced into a channel, the _anterior canal_ (as in Fig. 9); whilst where the mouth meets the base of the spire there may be a kind of notch which is termed the _posterior canal_. Most Gasteropods are _dextral_, that is to say, the mouth is to the right of the axis as you look at it; a few, however, are _sinistral_, or wound to the left (like _Physa_); whilst reversed varieties of both kinds are met with.

Gasteropods of the first order have comb-like gills placed in advance of the heart, and are hence termed PROSOBRANCHIATA. They are divided into two groups: (_a_) _Siphonostomata_ (Tube-mouthed), in which the animal has a long proboscis, and a tube, or siphon, from the breathing-chamber that passes along the anterior canal of the shell, which in this group is well developed. They have a horny operculum, or lid, with which to close the aperture. (_b_) _Holostomata_ (or Whole-mouthed). In these the siphon is not so produced, and does not want to be protected; accordingly the mouth of the shell is _entire_, _i.e._ has no canal. The operculum is horny or shelly. The former (group _a_) includes several families:

1. _Strombidae_, comprising shells, like the huge _Strombus_, or "Fountain-shell," which is so often used to adorn the mantelpiece or rockery, and from which cameos are cut.

2. The _Muricidae_, of which the _Murex_ (an extraordinary form of this is the "Venus' comb," _Murex tenuispina_, Fig. 9), the Mitre-shells, and the Red-Whelks (_Fusus_) are examples.

3. The _Buccinidae_, taking its name from its type, the Common Whelk (_Buccinum undatum_), and including such other forms as the Dog-Whelk (_Nassa_), the _Purpura_, the strange _Magilus_, and the lovely Harp-Shells and Olives (Fig. 10).

4. The _Cassididae_, or "Helmet-Shells." _Cassis rufa_, from West Africa, is noted as the best species of shell for cameo engraving; with it are classed the "Tun" (_Dolium_) and the great "Triton" (_Triton tritonis_), such as the sea-gods of mythology are represented blowing into by way of trumpet, and which are used by the Polynesian Islanders to this day instead of horns.

5. The _Conidae_, whose type, the "Cone-shell" (Fig. 11), is at once distinctive and handsome, but which in the living state is covered by a dull yellowish-brown periostracum that has to be carefully removed before the full beauties of the shell are displayed.

6. The _Volutidae_, embracing the Volutes and "Boat-shells" (_Cymba_).

7. The _Cypraeidae_, or Cowries (Fig. 12), which owe their high polish to the size of the shell-secreting organ (mantle), whose edges meet over the back of the shell, concealing it within its folds. With these is classed the "China-shell" (_Ovulum_).

The second group, or _Holostomata_, is divided into nineteen families, beginning with--

1. The _Naticidae_, whose type, the genus _Natica_, is well known to all shell-collectors through the common _Natica monilifera_ of our coasts.

2. The _Cancellariadae_, in which the shells are cancellated or cross-barred by a double series of lines running, one set with the whorls, and the other across them.

3. The _Pyramidellidae_, which are high-spired, elongated, and slender shells, with the exception of the genus _Stylina_, which lives attached to the spines of sea-urchins or buried in living star-fishes and corals. 4. The _Solaridae_ or "Staircase-shells," whose umbilicus is so wide that, as you look down it, the projecting edges of the whorls appear like a winding staircase. It is a very short-spired shell.

5. The _Scalaridae_, "Wentle-traps" or "Ladder-shells," which may be readily recognised from their white and lustrous appearance and the strong rib-like markings of the periodic mouths that encircle the whorls.

6. The _Cerithiadae_, or "Horn-shells," which are very high-spired, and whose columella and anterior canal are produced in the form of an impudent little tail, the effect of which, however, in the genus _Aporrhais_, or "Spout-shells," is taken away by the expanded and thickened lip.

7. In the next family, the _Turritellidae_, or "Tower-shells," the type Turritella is spiral; but in the allied form _Vermetus_, though the spire begins in the natural manner, it goes off into a twisted tube resembling somewhat an ill-made corkscrew. The mouth in this family is often nearly round.

8. The _Melaniadae_, and 9. The _Paludinidae_, are fresh-water shells. The former are turreted, and the latter conical or globular. Both are furnished with opercula, but the mouth in the first is more or less oval and frequently notched in front, while in the latter it is rounded and entire.

10. The _Litorinidae_, or Periwinkles, need no word from us.

11. The _Calyptraeidae_ comprise the "Bonnet-limpet," or _Pileopsis_, and "Cup-and-saucer-limpets" (_Calyptraea_). They may be described briefly as limpets with traces of a spire left. The genus _Phorus_, however, is spiral, and resembles a _Trochus_. They have been called "Carriers" from their strange habit of building any stray fragments of shell or stone into their house, thus rendering themselves almost indistinguishable from the ground on which they crawl.

12. The _Turbinidae_, or "Top-shells," are next in order, and of these the great _Turbo marmoreus_ is a well-known example, being prepared as an ornament for the whatnot or mantelpiece by removing the external layer of the shell in order to display the brilliant pearly nacre below. These mollusca close their mouths with a horny operculum, coated on its exterior by a thick layer of porcelain-like shelly matter. With them are classed the familiar _Trochus_ and other closely allied genera.

13. The _Haliotidae_ offer in the representative genus _Haliotis_, or the "Ear-shell," another familiar mantelpiece ornament.

14. The _Ianthinidae_, or "Violet-snails," that float about in mid-Atlantic upon the gulf-weed, and at certain seasons secrete a curious float or raft, to which their eggs are attached, are next in order, and are followed by--

15. The _Fissurellidae_, or "Key-hole" and "Notched limpets," whose name sufficiently describes them. To these succeed--

16. The _Neritidae_, an unmistakable group of globular shells, having next to no spire and a very glossy exterior, generally ornamented with a great variety of spots and bands.

17. The _Patellidae_, or true Limpets, are well known to every sea-side visitor: large species, as much as two inches across, are to be found on the coast of Devon, but these are pigmies compared with a South American variety which attains a foot in diameter.

18. The _Dentaliadae_, represented by the genus _Dentalium_, or "Tooth-shell," are simply slightly curved tubes, open at both ends and tapering from the mouth downwards, and cannot be mistaken.

19. Lastly, we have the _Chitonidae_, whose single genus _Chiton_ possesses shells differing from all other mollusca in being composed of eight plates overlapping each other, and in appearance reminding one of the wood-louse. This animal is not only like the limpet in form but also in habits, being found adhering to the rocks and stones at low-water.

Order II.--PULMONIFERA. Contains the air-breathing _Gasteropods_, and to it consequently belong all the terrestrial mollusca, though some few aquatic genera are also included. The members of this order have an air-chamber instead of gills, and are divided into two groups, (_a_) those without an operculum, and (_b_) those having an operculum. Foremost in the first group stands the great family--

1. _Helicidae_, named after its chief representative, the genus _Helix_. It also includes the "Glass-shell" (_Vitrina_), the "Amber-shell" (_Succinea_), and such genera as _Bulimus_, _Achatina_, _Pupa_, _Clausilia_ (Fig. 13), etc., which differ from the typical _Helix_ in appearance, possessing as they do comparatively high spires.

2. The _Limacidae_, or "slugs," follow next; of these only one, the genus _Testacella_, has an external shell stuck on the end of its tail; the rest have either a more or less imperfect shell concealed underneath the mantle, or else none at all.

3. The _Oncidiadae_ are slug-like, and devoid of shell.

4. The _Limnaeidae_ embrace the "Pond-snails," chief of whom is the well-known, high-spired _Limnaea stagnalis_. Other shells of this family associated with _Limnaea_ are, however, very different in shape; for instance, _Physa_ has its whorls turning to the left instead of to the right; _Ancylus_ (Fig. 24), or the freshwater limpet, is of course limpet-like; while _Planorbis_, or the "Coil-shell," is wound like a watch-spring.

5. The _Auriculidae_ includes both spiral shells, such as _Auricula_ and _Charychium_, and a limpet-like one _Siphonaria_.

At the head of group _b_ stands 1, _Cyclostomidae_. _Cyclostoma elegans_ is a common shell on our chalk-downs, and well illustrates its family, in which the mouth is nearly circular. Foreign examples of this genus are much esteemed by collectors. The other two families are, (2) _Helicinidae_ and (3) _Aciculidae_.

Order III.--OPISTHOBRANCHIATA. These animals carry their gills exposed on the back and sides, towards the rear of the body. Only a few have any shell. 1. The _Tornatellidae_, which have a stout little spiral shell. 2. The _Bullidae_, in which the spire is concealed (Fig. 26). 3. The _Aplysiadae_, where the shell is flat and oblong or triangular in shape. The remaining families are slug-like and shell-less.

Order IV.--NUCLEOBRANCHIATA. Derives its name from the fact that the animals constituting it have their respiratory and digestive organs in a sort of nucleus on the posterior part of the back, and covered by a minute shell. As they are pelagic, the shells are not readily to be obtained. They are divided into two families, _Firolidae_ and _Atlantidae_.

CLASS III.--PTEROPODA. Like the last, these pretty little mollusca are ocean-swimmers. The members of one division of them, to which the _Cleodora_ belongs, is furnished with iridescent external shells.

CLASS IV.--The LAMELLIBRANCHIATA (Plate-gilled), or CONCHIFERA (Shell-bearing), includes the mollusca commonly known as "bivalves," the animal being snugly hidden between two more or less closely fitting shelly valves. The oysters, cockles, etc., are examples of this class. The two valves are fastened together near their points, or beaks (technically called _umbones_), by a tough elastic ligament, sometimes supplemented by an internal cartilage. If this be severed and the valves parted, it will be found that in most cases they are further articulated by projecting ridges or points called the _teeth_, which, when the valves are together, interlock and form a hinge; the margin of the shell on which the teeth and ligament are situated is termed the _hinge-line_. A bivalve is said to be _equivalve_ when the two shells composing it are of the same size, _inequivalve_ when they are not. If the umbones are in the middle, the shell is _equilateral_ (Fig. 15); but _inequilateral_ when they are nearer one side than the other (Fig. 16). If the shell be an oyster or a scallop, you will find on the inside a single circular scar-like mark near the centre; this is the point to which the muscles that close the valves and hold them so tightly together are attached. In the majority of bivalves, however, there are two such muscular impressions, or scars, one on either side of each valve of the shell. The former group on this account are often called _Monomyaria_ (having one shell-muscle), and the latter _Dimyaria_ (having two shell-muscles). In the last named the two muscular impressions are united by a fine groove (or _pallial-line_), which in some runs parallel to the margin of the shell (Fig. 15), whilst in others it makes a bend in (_pallial-sinus_) on one side of the valve towards the centre (Fig. 16). In Monomyaria it will be found running parallel to the margin of the shell. It marks the line of attachment of the mantle or shell-secreting organ of the animal to the shell which grows by the addition of fresh matter along its edges, so that the concentric curved markings so often seen on the exterior correspond in their origin with the periodic mouths of the Gasteropods. The bivalves are all aquatic, and many bury themselves in the sand or mud by means of a fleshy, muscular foot. These are furnished with two siphons, or fleshy tubes, sometimes united, sometimes separate, through which they respire, drawing the water in through one and expelling it by the other. Those kinds whose habit it is to bury themselves below the surface of the mud or sand are furnished with long retractile siphons, and to admit of their withdrawal into the shell, the mantle is at this point attached farther back, giving rise to the _pallial-sinus_ above described; this sinus is deeper as the siphons are proportionately longer, and in many cases, too, the valves do not meet at this point when the shell is closed.

Attention to these particulars is necessary when arranging your bivalves, as on them their classification depends, the class being divided into--

_a._ ASIPHONIDA (Siphonless).

_b._ SIPHONIDA _Integro-pallialia_ (with Siphons).--Pallial-line entire.

_c._ SIPHONIDA _Sinu-pallialia_ (with Siphons).--Sinus in pallial-line.

DIVISION _a_.--ASIPHONIDA--is next subdivided into--

1. The _Ostreidae_, or oysters, which are deservedly a distinct family in themselves.

2. The _Anomiadae_, comprising the multiform and curiously constructed _Anomia_, with the "Window-shells" (_Placuna_).

3. The _Pectinidae_, taking its name from the genus _Pecten_, or "Scallop-shells," of which one kind (_P. maximus_) is frequently to be seen at the fishmongers' shops. The "Thorney oysters" (_Spondylus_) take rank here, and are highly esteemed by collectors, one specimen indeed having been valued at L25!

4. The _Aviculidae_, or "Wing-shells," among which are numbered the "Pearl-oyster" of commerce (_Meleagrina margaritifera_). The strange T-shaped "Hammer oyster" belongs to this family, as does also the _Pinna_. The Pinnas, like the mussels and some other bivalves, moor themselves to rocks by means of a number of threads spun by the foot of the mollusc, and termed the _byssus_, which in this genus is finer, more silky, than in any other, and has been woven into articles of dress.

5. The _Mytilidae_, or mussels, including the _Lithodomus_, or "Date-shell," which bores into corals and even hard limestone rocks.

6. The _Arcadae_, or "Noah's-ark-shells," characterized by their long straight hinge-line set with numerous very fine teeth (Fig. 17). The "Nut-shell" (_Nucula_) belongs to this family.

7. The _Trigoniadae_, whose single living genus, the handsome _Trigonia_ (Fig. 18), is confined to the Australian coast-line, whereas in times now long past they had a world-wide distribution.

8. The _Unionidae_, comprising the fresh-water mussels.

DIVISION _b_.--SIPHONIDA _Integropallialia_.

1. The _Chamidae_, represented by the reef-dwelling _Chama_.

2. The _Tridacnidae_, whose sole genus _Tridacna_ contains the largest specimen of the whole class of bivalves, the shells sometimes measuring two feet and more across.

3. The _Cardiadae_, or cockles.

4. The _Lucinidae_, in which the valves are nearly circular, and as a rule not very attractive in appearance, though the "Basket-shell" (_Corbis_) has an elegantly sculptured exterior.

5. The _Cycladidae_, whose typical genus _Cyclas_, with its round form and thin horny shell, is to be found in most of our ponds and streams.

6. The _Astartidae_, a family of shells having very strongly developed teeth, and the surface of whose valves is often concentrically ribbed.

7. The _Cyprinidae_, which have very solid oval or elongated shells and conspicuous teeth (Fig. 19). The "Heart-cockle" (_Isocardia_) belongs to this family.

DIVISION _c_.--SIPHONIDA _Sinu-pallialia_.

1. The _Veneridae_. The hard, solid shells of this family are for elegance of form and beauty of colour amongst the most attractive a collector can posses. Their shells are more or less oval and have three teeth in each valve (Fig. 20).

2. The _Mactridae_ are somewhat triangular in shape, and may be at once recognised by the pit for the hinge-ligament, which also assumes that form, as seen in the accompanying figure of _Lutraria elliptica_ (Fig. 21).

3. The _Tellinidae_ comprise some of the most delicately tinted, both externally and internally, of all shells. In some, coloured bands radiate from the umbones, and well bear out the fanciful name of "Sunset shells" bestowed upon them. Their valves are generally much compressed.

4. The _Solenidae_, or "Razor-shells," rank next, and are readily recognised by the extreme length of the valves in proportion to their width, and also by their gaping at both ends.

5. The _Myacidae_ or "Gapers," have the siphonal ends wide apart (in the genus _Mya_ both ends gape), and are further characterized by the triangular process for the cartilage, which projects into the interior of the shell. One valve (the left) is generally smaller than the other.

6. The _Anatinidae_ have thin, often inequivalve pearly shells. The genus _Pandora_ is the form most frequently met with in collections.

7. The _Gastrochaenidae_ embraces two genera (_Gastrochaena_ and _Saxicava_) of boring mollusca, which perforate shells and rocks, and also, the remarkable tube-like "Watering-pot-shell" (_Aspergillum_) which is hardly recognisable as a bivalve at all.

8. The _Pholadidae_ concludes the list of bivalves, and comprises the common rock-boring Pholas (Fig. 22) of our coasts and the wood-boring shipworm "Teredo" (Fig. 23).

* * * * *

Although the _Brachiopoda_, or "Lamp-shells," are not true mollusca, they are not very far removed from them, and are so often to be found in cabinets that it will not do to pass them over, especially since in past times they were very abundant, an enormous number occurring in the fossil state. Only eight genera are now living. Shells belonging to this class are readily recognised by the fact of one valve being larger than the other, and possessing a distinct peak, the apex of which is perforated. The _Terebratulidae_ are the most extensive family of this class.

HOW TO ARRANGE THE SHELLS IN THE CABINET.

When you have arranged your specimens in the order above indicated, proceed to place them in your boxes, arranging and labelling them after the manner shown in the accompanying diagram.

On the lid, or on a slip of paper or card placed at the head of your columns of trays, write the class and order, with its proper number (I., II., etc., as the case may be); then at the top of your left-hand column place the family and its number, and under it the name of the first genus. The species (one in each tray) come next, then the name of the next genus following it, succeeded by its species, and so on.

The object of the young collector should be to obtain examples of as many _genera_ as possible, since a collection in which a great number of genera are represented is far more useful and instructive than one composed of a great many species referable to but few genera. He will also find it very convenient to separate the British Shells from his general collection, sub-dividing them for convenience into "Land and Fresh-water," and "Marine." Of these he should endeavour to get every species, and even variety, making the thing as complete as possible. Or a separate collection may be made of all those kinds which he can find within a certain distance of his own home. A collection of this sort possesses, in addition to its scientific worth, an interest of its own, owing to the local associations that invariably connect themselves with it.

TABLE OF SOME OF THE MORE IMPORTANT GENERA, SHOWING THE APPROXIMATE NUMBER OF SPECIES BELONGING TO EACH GENUS AND THEIR DISTRIBUTION.

CLASS I.--CEPHALOPODA.

ORDER I.--Dibranchiata.

Section A.--_Octopoda._

Family. Genus. No. of Species. Distribution.

1. Argonauta 4 Tropical seas.
2. Octopus 46 Rocky coasts in temperate and
tropical regions.
Section B.--_Decapoda_.

3. Loligo 19 Cosmopolitan.
4. Sepia 30 On all coasts.
5. Spirula 3 All the warmer seas.

ORDER II.--_Tetrabranchiata_.

6. Nautilus 3 or 4 Chinese Seas, Indian Ocean,
Persian Gulf.

CLASS II.--GASTEROPODA.

ORDER I.--Prosobranchiata.

Division _a_.--_Siphonostomata._