A conchological manual

by G. B. Sowerby

After describing the nature of the science and defining its objects, we shall proceed to explain the structure of those objects, and the manner of their growth. We shall then enter somewhat minutely into the principles of classification, the distinctions upon which they are founded, and some of the technical terms used to express them. After which we shall pass through the arrangement of Lamarck, defining the general divisions adopted under the terms of "Classes, Orders, and Families," as far as they are capable of definition. The subdivision of the latter into genera will only be entered into so far as to enumerate the principal of them, the more minute descriptions being reserved for the alphabetical part of the work.

Let none be discouraged by the number of generic distinctions proposed and adopted in modern times; for if well defined, they will be found to facilitate rather than encumber the science. The knowledge of species must be the foundation of every system, and the greater their number, the more necessary it becomes to subdivide them; if, for instance, all the species now known were to have been included in the 50 genera of Linnæus, a single genus would have contained many hundreds of incongruous species, in which case it would be much more difficult to remember them, than if they were to be divided into a far greater number of genera. Every well marked division, however arbitrary its limits, tends to simplify the subject, and to facilitate the researches of the student.

NATURE OF THE SCIENCE.

Conchology is the study of shells, viewed and described as to what they are either in themselves, or in relation to the soft, inarticulate animals which produce them, and of which they form a part. These animals are called Mollusca, and perhaps the best general description of them will be found in De Blainville's "Manuel de Malacologie et de Conchyliologie." The following is a translation, "Animal in pairs, the body and its appendages soft, inarticulate (not jointed), enveloped in a muscular skin, commonly called the mantle, which is extremely variable in form, and has developed either within or upon it a calcareous portion, consisting of one or several pieces, commonly called a SHELL."

The term Mollusca was formerly restricted to those soft animals which were destitute of shells, although possessing in other particulars, the characters described above, and it was used in order to distinguish them from the Testacea, which were covered or internally supported by calcareous parts. 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.

The nearest approach to correctness, and the most philosophical method of study will be found in the modern system, adopted by Lamarck and his followers, of observing these animals as a whole, and arranging them according to the assemblage of characters which they present; of course taking into consideration the existence or non-existence, form and structure of the shell, on the same principle, which, in arranging the vertebrated animals would lead us to study the hair, hoof, nails, claws, &c. as well as the other parts.

At the same time, it must be admitted that there are many private collectors of Shells who would find it a difficult, if not impossible task to study minutely and successfully the soft parts of the Mollusca. 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. Let it also be remembered, that if shells had not been rendered commercially valuable, by the zeal and emulation manifested by mere Conchologists for the possession of rare specimens, few travelling merchants and sea captains would have thought them worthy of a corner in their cabins. In this case, few specimens being brought to the country, the more Philosophical Naturalist would have been left without the means of obtaining materials to work upon, or of attracting public attention to his favourite pursuit.

On account of these and other considerations, it has been thought advisable that the present undertaking should bear a purely conchological character. 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. And the conviction must be expressed, that if ever a complete Natural System shall be formed it will result from the labours of the last mentioned class of naturalists.

DEFINITION OF A SHELL.

Before entering minutely into the description of shells, it will be necessary to distinguish from the true testaceous Mollusca two kinds of animals which have formerly been associated with them. Of these, the first is the class of Crustacea, consisting of crabs, crayfish, &c. These differ from shell-fish, not only in structure and chemical composition, but also in the fact that the animal has jointed limbs, and that the substance of the flesh is inseparable from the hard external covering, which invests each particular joint as with a sheath; whereas the Molluscous animal is but partially attached to its shell, from which it possesses the power of partly withdrawing and returning. The second class is that to which the sea-urchin, or Echinus, belongs, of which there are many genera and species. The testaceous covering of Echini is composed of a number of small pieces, placed edge to edge, forming a more or less globular external covering to the flesh, which is supported in the centre by a number of bones leaning upon each other in a pyramidal form. The test is of a fibrous texture, guarded on the outside with moveable spines, which turn on ball and socket joints.