The _Pelagia_, as the name implies, belong to the deep sea. _P. noctiluca_ has a transparent, glass-like disk, of a reddish-brown colour and warty appearance. It is found in the Mediterranean, about the coast near Nice, and is still more plentiful on the coast of Sicily, and on the African coast. Another species, _P. panopyra_, is very common in the Atlantic and Pacific, between the Tropics. The naturalist Lesson met whole banks of them in the equatorial ocean, about the twenty-seventh degree north latitude and the twenty-second degree west longitude. During the night, this species emits a brilliant phosphoric light, and living individuals, which Lesson succeeded in preserving, exhibited great luminosity in the dark. This medusa is remarkable for its semi-spherical disk, slightly depressed, umbilicate at the summit, a little compressed at the edges, and densely bristling on the surface with small elongated warts, but regularly festooned along the edges. In colour it is a delicate rose. * * * * * The animals which constitute this class of Zoophytes, and, in former times, so curious and so imperfectly known, were designated _Polypomedusæ_, in order to remind us that at one time they were called Medusæ, and at others ranged among the Polyps. It has, however, been recently discovered that, shortly after they issue from the egg, these zoophytes show themselves in the form of polyps, and that, at a later period, they assume the animal form, to which we give the name of medusæ. These animals are, then, true proteans: hence the very considerable difficulty of studying them--difficulties which have long reduced naturalists to despair. Even now their history is too obscure and too complicated to justify us in presenting it, except in its general features. We shall, therefore, content ourselves here with a description of the best known species of the class only--those, namely, which have particularly attracted the attention of naturalists, and which are, at the same time, of a nature to interest our readers. The class of Discophoræ may be divided into four orders or families, namely:-- I. THE HYDRAIDÆ, having single, naked, gelatinous, sub-cylindrical, but very contractile stems, mutable in form, mouth encircled with a single series of granulous filiform tentacula. II. SERTULARIADÆ, plant-like and horny, rooted and variously branched, filled with semi-fluid organic pulp, the polyps contained within sessile cells disposed along the sides of the main stem or branchlets, but never terminal. III. MEDUSADÆ. Umbel hemispherical, with marginal tentacula; having eight eyes covered by lobes, four ovaries, four cells, four fringed arms, a central opening, and four lateral openings.