It is scarcely more than a hundred and twenty years ago, that the existence of this numerous order of microzoa was first made known to naturalists by _Beccarius_, who detected a considerable number of species in the sand on the shores of the Adriatic. But the structure of the animals that secreted these shells is a discovery of comparatively modern date. The early collectors classed these microscopic bodies with the shells of true mollusca; and even M. D'Orbigny, whose elaborate researches justly constitute him a high authority in this branch of natural history, in his first memoir, in 1825, described the involuted discoidal forms as Cephalopoda. This error was corrected by the investigations of M. Dujardin, who in 1835 satisfactorily demonstrated that the Foraminifera are animals of the most simple structure, and entirely separated by their organization from the Mollusca. But the true nature of this class is so little understood by British collectors of fossil shells,--of course I mean the uninitiated, and the amateur naturalist, for whose use these unpretending pages are designed,--that in order to invest the study of the fossil species with the interest which a knowledge of the structure and economy of the living originals can alone impart, I must give a history of the recent forms somewhat in detail, taking M. D'Orbigny as my chief authority.[310] [310] The best work for the student to consult is M. D'Orbigny's "Foraminifères Fossiles du Basse Tertiaire de Vienne, Autriche." Paris, 1846. 1 vol. 4to. with plates. I rejoice to learn that a Monograph on the British Foraminifera is in preparation by Dr. Carpenter and Professor Williamson: than whom there are none more competent. [Sidenote: FORAMINIFERA.] The Foraminifera are marine animals of low organization, and, with but few exceptions, extremely minute: in an ounce of sea-sand between three and four millions have been distinctly enumerated. When living, they are not aggregated, but always individually distinct; they are composed of a body, or vital mass, of a gelatinous consistence, which is either entire and round, or divided into segments, placed either on a simple or alternate line, or coiled in a spiral, or involuted round an axis. This body is covered with an envelope or shell, which is generally testaceous, rarely cartilaginous, is modelled on the segments, and follows all the modifications of form and contour of the body. From the extremity of the last segment there issue sometimes from one, sometimes from several openings of the shell, or through the numerous pores or foramina, very elongated, slender, contractile, colourless, filaments, more or less divided and ramified, serving for prehension, and capable of entirely investing the shell. The body varies in colour, but is always identical in individuals of the same species; it is yellow, ochreous, red, violet, blue, &c.