George Brettingham Sowerby II

“ The Science of Conchology affords a very delightful and instructive amusement for the leisure hours of those who, retiring occasionally from the gaieties of fashionable life, seek pleasure in the quiet contemplation of some of the smaller, but not less wonderful operations of creative wisdom. ”

“ In counting the whorls of which the spire consists, we commence at the apex, and reckon downwards to the last, or body whorl. The spire is described as being long or short in relation to the aperture: in which case, all that is above the aperture is measured with the spire. Its apex requires particular notice, as the character of the whole shell frequently depends upon the particulars observable in this part. It is sometimes obtuse, or blunt; sometimes acute, or sharp. ”

“ When this is dry and become sufficiently hard, it is lined by a more calcareous secretion; and these together form a new layer, which is followed by others in succession; each new layer being larger than the one that preceded it until the whole being complete, the full-grown animal is invested with a shell commensurate with its own proportions. Thus from the apex or nucleus the formation proceeds, as it were, downwards, taking the shape of the part which secretes it, on which it is in a manner moulded. ”

“ For this purpose, we must suppose the animal to be living and creeping along the bed of the sea by means of its foot; where this foot protrudes, will be the ventral margin, and the opposite part the dorsal margin of the shell. There will then be a valve on each side; and if we further suppose the animal to be walking forward with its back to the observer, the right and left valves will correspond with his right and left sides. ”

“ The Nautilus, the Spirula, the Scaphite, and the Ammonite are the leading types of this form; but when we use the term symmetrical, in reference to these, the word must not be understood in its strictest sense, for no shell is perfectly symmetrical: but it means that there is no perceptible difference in the proportion of the two sides; as in the human body, the right side is larger and more powerful than the left, yet to a degree so small that it gives no apparent bias to the figure. ”

“ Where there is but one adductor muscle, there will be but one of these impressions near the centre of each valve, but in the Dimyaria, where there are two, the impressions are seen, one on the anterior, and one on the posterior of each valve, just below the hinge lamina. They are sometimes complex, that is composed of several portions in a group; but in general, they are simple and well defined.
They are also described as large or small, in proportion to the size of the shell; regular or irregular in form. ”

“ The operculum always consists of more than one piece, generally of two pairs: they are either articulated to each other by serrated edges, and placed against each other conically, as in Balanus, or they lie flat in two pairs against each other. Through the ventral pair the cirrhi protrude.
The parietal valves, composing the principal part of the shell, vary in number, form and position. The anterior valves are placed on the same side with the cirrhi; the posterior, those on the opposite side; and those which remain between on each side are the lateral valves. ”

“ The aperture of many species of shells remains constantly open; but in a great number of species it is occasionally closed, whenever the animal is retracted within the shell, by a calcareous or horny piece called the operculum. ”

“ It is necessary to attend, as far as means and opportunity will allow, to all the points of difference, both in the shell and in the animal, in order to form, and in some instances even to appreciate, a generic or larger distinction. ”

“ In the system of Linnæus, the soft portions are first arranged under the general designation of "Vermes Mollusca," and described without regard to the presence, absence, or character of the shells; and then the shells are separately characterized under the appellation of "Vermes Testacea," without any further notice of the animal, than an indication of the genus to which it belongs; thus the animal of Cypræa is said to be a Limax, and that of Tellina a Tethys. ”

“ When the breadth is spoken of, the distance between the most convex parts of both valves, when closed, is intended; but when an expression implying thickness is used, it refers to the substance of each valve: it is important to bear this in mind, as many persons have been misled by descriptions in which the distinction has not been attended to. Glycimeris (fig. 67 in the plates) is a thick shell, but Anatina (fig. 69 in the plates) is a broad one. ”

“ Those which are placed immediately below the umbones, and seem to take their rise from beneath them, are called cardinal teeth; those at a distance from the umbones, which are seen to lie along the upper margin of the shell are named lateral teeth. ”

“ And although this consideration belongs more especially to the study of the animal itself, yet the habits of the animal materially influence the structure of the shell.
The Terrestrial or Land Molluscs live on land, breathe air, and feed on plants and trees.—Those who find pleasure in horticultural pursuits will at once call to mind a too familiar example of these Molluscs in the common garden snail. ”

“ When there is neither notch nor canal, anteriorly or posteriorly, interrupting the edge of the aperture, it is described as entire. When there is a notch or sinus at the anterior extremity, it is said to be emarginated. When the edge of this notch is expanded, and drawn out in the form of a beak, it is said to be canaliferous, or to have a canal. ”

“ On examining this piece, it will be observed that it is not formed in regular layers like the rest of the shell; while the true operculum is of a regularly laminated structure, having a nucleus and receiving obliquely deposited additions, either in a lateral spiral or concentric direction. It is attached to the posterior part of the foot on the upper surface; and when the animal retires within its shell, that part of the foot enters last, drawing the operculum after it, and thus closing the aperture. ”

“ Ladies, for instance, could not be expected to handle with pleasure and perseverance, these fleshy substances, which in order to be preserved from putrefaction, must be kept in spirits; and yet such persons may, with improvement and advantage to their own minds, enjoy the interesting and scientific amusement of studying and arranging the clean and beautiful natural objects which are so easily preserved, and so exquisitely curious in their structure. ”

“ The peculiarities of the shells alone being detailed for the assistance of those who collect and study them, while at the same time, in deciding upon their affinities and places, in the arrangement, it will be necessary to take advantage of the conclusion to which those have arrived, who have studied the animal in all its parts. ”

“ Supposing, however, that the person who desires to learn the science, possesses a small parcel of unarranged and unnamed shells, without any previous acquaintance with the subject, the following introductory explanations, are drawn up with the view of enabling him, without further assistance, to obtain a general insight into its principles, equal to that of those who have studied it long and laboriously. ”

“ It runs near the ventral margin from one muscular impression to the other, sometimes in a smooth continuous line or band, and sometimes in an interrupted series of small impressions. Near the point of union with the posterior muscular impression, there is sometimes a more or less considerable winding inwards towards the centre of the shell, and back again towards the point of union. This is named the sinus, and is distinguished as being angular or rounded, large or small, according to the species. ”

“ It may be as well here to advise those who are forming a collection to be very particular in every practicable instance to have the shells properly named at the time of purchasing; as it will save much trouble, and materially assist in the attainment of the desired object. To this end, recourse should be had to those naturalist tradesmen, who unite the attainment and diffusion of real scientific knowledge with their commercial pursuits. ”

“ And the learner may also be reminded that the Limpets themselves are not all regular in their form: for as they adhere to rocks and other rough surfaces, and are so little locomotive, in many instances they partake of the inequalities of the surface, and conform to its irregularities. ”

“ The epidermis of these is generally of a thick, close-grained character, and they are subject to corrosion near the umbones. There are but few genera of fresh-water shells besides the Uniones, among bivalves, and the "Melaniana" among univalves. Concerning the former it may be observed, that they are all pearly within, and the colour of the thick horny coating embraces all the varieties of brownish and yellowish green.
The Marine, or sea-shells, belong to all the classes and orders, and include by far the greater number of species. ”

“ These are generally locomotive, and consequently free from those obstructions in growth occurring to stationary shells, which being confined in a particular position, or to a particular spot, modify their shape according to the substance with which they come in contact, and thus become irregular. ”

“ When these rests take place at frequent periods, the varices will of course be numerous as in Harpa and Scalaria. They occur at regular or irregular distances, varying in shape and other characters. When the varices occur at regular intervals, and form a connected ridge from whorl to whorl up the spire, they are said to be continuous, as in Ranella ”

“ The third kind are termed coronular by De Blainville, and compose the order Sessile Cirripedes of Lamarck; they consist of a number of valves placed against each other side by side in a circle, supported on a plate, or tube, or cup, and closed by an operculum composed of two or more valves.
The basal support is sometimes thick and flat, sometimes forming an elongated tube, and sometimes hollowed out into a cup. In other species it is altogether wanting. ”