The Bicidium (Fig. 14), our parasitic Actinia, is to be sought for in the mouth-folds of the Cyanea, our common large red Jelly-fish. In any moderate-sized specimen of the latter from twelve to eighteen inches in diameter, we shall be sure to find one or more of these parasites, hidden away among the numerous folds of the mouth. The body is long and tapering, having an aperture in the extremity, the whole animal being like an elongated cone, strongly ribbed from apex to base. At the base, viz. at the month end, are a few short, stout tentacles. This Actinia is covered with innumerable little transverse wrinkles (see Fig. 14), by means of which it fastens itself securely among the fluted membranes around the mouth of the Jelly-fish. It will live a considerable time in confinement, attaching itself, for its whole length, to the vessel in which it is kept, and clinging quite firmly if any attempt is made to remove it. The general color of the body is violet or a brownish red, though the wrinkles give it a somewhat mottled appearance. _Halcampa_. (_Halcampa albida_ AG.) Strange to say, the Actiniæ, which live in the mud, are among the most beautifully colored of these animals. They frequently prepare their home with some care, lining their hole by means of the same secretions which give their slimy surface to our common Actiniæ, and thus forming a sort of tube, into which they retire when alarmed. But if undisturbed, they may be seen at the open door of their house with their many colored disk and mottled tentacles extending beyond the aperture, and their mouth wide open, waiting for what the tide may bring them. By the play of their tentacles, they can always produce a current of water about the mouth, by means of which food passes into the stomach. We have said, that these animals are very brightly colored, but the little Halcampa (Fig. 15), belonging to our coast, is not one of the brilliant ones. It is, on the contrary, a small, insignificant Actinia, resembling a worm, as it burrows its way through the sand. It is of a pale yellowish color, with whitish warts on the surface. [Illustration: Fig. 15. Halcampa albida; natural size.] * * * * * MADREPORIANS. _Astrangia_. (_Astrangia Danæ_ AG.) In Figure 16, we have the only species of coral growing so far north as our latitude. Indeed, it hardly belongs in this volume, since we have limited ourselves to the Radiates of Massachusetts Bay,--its northernmost boundary being somewhat to the south of Massachusetts Bay, about the shores of Long Island, and on the islands of Martha's Vineyard Sound. But we introduce it here, though it is not included under our title, because any account of the Radiates, from which so important a group as that of the corals was excluded, would be very incomplete. [Illustration: Fig. 16. Astrangia colony; natural size.]