The _Isis corolloïdis_ of Oceania has a coral with numerous slender branches, furnished with cylindrical knots at intervals, contracted towards the middle, finely striated, and rose-coloured. _Isis_ _hippuris_, represented in Fig. 46, has a singular resemblance to the Common Mare's Tail (_Hippuris vulgaris_). [Illustration: Fig. 46. Isis hippuris.] Four other species of Isidians are known. The same family includes the genera of _Melitæa_ and _Mopsea_, which, however, our limits forbid us to describe. CORALLINÆ. The group of Corallines consist of a single genus, _Corallium_, having a common axis, inarticulate, solid, and calcareous, the typical species of which furnishes matter hard, brilliant, and richly coloured, and much sought after as an object of adornment. This interesting zoophyte and its product require to be described with some detail. From very early times, the coral has been adopted as an object of ornament. From the highest antiquity, also, efforts were made to ascertain its true origin, and the place assignable to it in the works of Nature. Theophrastus, Dioscorides, and Pliny considered that the coral was a plant. Tournefort, in 1700, reproduced the same idea. Réaumur slightly modified this opinion of the ancients, and declared his opinion that the coral was the stony product of certain marine plants. Science was in this state when a naturalist, who has acquired a great name, the Count de Marsigli, made a discovery which threw quite a new light on the true origin of this natural product. He announced that he had discovered the flowers of the coral. He represented these flowers in his fine work, "La Physique de la Mer," which includes many interesting details respecting this curious product of the ocean. How could it be longer doubted that the coral was a plant, since he had seen its expanded flowers? No one doubted it, and Réaumur proclaimed everywhere the discovery of the happy Academician. Unhappily, a discordant note soon mingled in this concert. It even emanated from a pupil of Marsigli!