Part 4

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. 3b); 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.