name given by the ancients to a species of marble dug near Megara, and remarkable for containing a great number of sea-shells, and other marine bodies, immersed in it.

Conchoïd, in Geometry, the name of a curve, given to it by its inventor Nicomedes. See Fluxions.

Conchology,

Is that department of natural history which treats of terebraceous animals. In the Linnean arrangement it constitutes the third order of the class of Vermes. This is the order terrestria, of which we propose to lay before our readers a pretty full view in the present treatise. The peculiarity and extent of this order of animals have induced us to consider it in a separate treatise, by which means we shall avoid swelling out to an an inconvenient magnitude, the clasps of Verme which will be treated of in its proper place in the course of the work.

The fine polish, splendid colours, and elegant form of shells, have been long admired, and have procured for them a conspicuous place in the cabinets of the curious. Indeed in this respect, mankind have discovered no small degree of folly and extravagance, in the high price which has been given for rare and beautiful shells, and often only on account of their rarity. But the study of conchology acquires a higher degree of importance and utility in another view. In many parts of the world, different kinds of terebraceous animals are employed as an excellent and nutritious food; and some tribes supply the table with a delicate luxury. Different shells furnish employment to ingenuity and art, in the manufacture of mother-of-pearl for various purposes; and the pearl itself, so much sought after as an ornament of drels, and often the rival of the richest gems, in the estimation of mankind, is the production of terebraceous animals. Its nature and mode of formation, therefore, cannot fail to be objects of curious investigation. But terebraceous animals and their productions, are not only beneficial and ornamental; some are found to be highly pernicious. The snail ravages the garden and the field, and marks its progress with the destruction of some of the fairest of the vegetable tribes; while the ship-worm is justly the dread of the mariner; feculence, as it were, in its insignificance, humbles the glory and pride of man; and labouring in secret, demolishes the noblest efforts of ingenuity. In these views, then, the economy and habits of terebraceous animals, which at first sight might appear a barren and useless pursuit, become an important and beneficial subject of investigation. The following chapters, therefore, shall be occupied in the classification and natural history of this tribe of animals.

CHAP. I. HISTORY OF CONCHOLOGY.

THE few scattered fragments concerning the natural history of shells, or terebraceous animals, which are to be found in the writings of the ancients, when compared with the more extended and systematic labours of the moderns, are so unimportant and inaccurate, that it would be altogether superfluous to trouble our readers with an account of the information which they contain. It appears, however, from the works of Aristotle and Pliny, the great naturalists of Greece and Rome, that the study of conchology was not entirely neglected in their time. It appears too, that admirers and collectors of shells were not then wanting. Scipio and Laelius, we are informed, found a relaxation from the toils and cares of war and government, by indulging in this elegant amusement (a).

Nor will it be attended with much advantage, to give a particular account of the works of the earlier writers on this subject, among the moderns. These are Gmelin, Johnston, Rondeletius, Aldrovandus, Belonius, Wormius, and some other authors, who cultivated this department of natural history, and accompanied their descriptions with figures, illustrative of the objects which they described.

The first author who attempted a systematic division of shells, according to their external form and characters, was John Daniel Major, professor of medicine in the university of Kiel in Holstein. His method is published at the end of his curious and interesting remarks on the treatise concerning the purpura of Fabius Columna, printed at Kiel in 1675. The system of the German naturalist was followed by that of our countryman Dr Lister, on a more extended and improved plan, which was published ten years after. Succeeding naturalists turned their attention to the study of conchology, and to the improvement of the classification of the numerous objects of this department of natural history. Such were Buonanni, Rumfius, Langius, Breyerius, Tournefort, Gualtieri, D'Argenville, Klein, Linnaeus, Adanson, Geoffroy, and Muller.

We shall here exhibit some of the most celebrated systems of conchology which have been proposed by writers on this subject. This, we trust, will not be unacceptable to our readers, and particularly as the works of these authors are in few hands, and therefore become less accessible.

I. The first general arrangement of shells is that System of published by Dr Lister in a work with the following title. Martini Lister, M. D. Historiae seu Synopsis methodicae Conchyliorum libri quatuor, continentes 1057 figuras a nitidissime incultis, a Susanna et Anna Lister depictis. Londini, 1685—1688, folio. A second edition of the same work was published at Oxford in 1770, with additional figures.

SYSTEM OF LISTER.

LIB. I. De Cochleis Terrestribus.

PARS I. De Buccinis et Turbinibus terrestribus.

Sect. 1. De Buccinis terrestribus a sinistra dextrorum tortilibus, levibus, edentulis.

Sect. 2. De Buccinis terrestribus a sinistra dextrorum tortilibus, edentulis, striatis.

Sect. 3. De Buccinis terrestribus a sinistra dextrorum tortilibus, apertura dentata.

Sect. 4. De Buccinis terrestribus a dextra sinistrorum tortilibus, apertura plana.

Sect. 5. De Buccinis terrestribus a dextra sinistrorum tortilibus, apertura dentata.

Sect. 6. De Turbinibus terrestribus cochleiformibus, id est compactiore figura.

(a) Laelium et Scipionem conchas et umbilicos ad Cajetam et ad Laurentum legere consueverat, et ad omnem animi remissionem ludumque descendere. Cic. de Orat. lib. ii. Chap. I.