THE connection between Brainstones, Mushroom Corals, and other Madrepores abounding on Polynesian reefs, and the “Sea Anemones,” which have lately become so familiar to us all, can be seen by comparing our comparatively insignificant C. Smithii with our commonest species of Actinia and Sagartia. The former is a beautiful object when the fleshy part and tentacles are wholly or partially expanded. Like Actinia, it has a membranous covering, a simple sac-like stomach, a central mouth, a disk surrounded by contractile and adhesive tentacles. Unlike Actinia, it is fixed to submarine bodies, to which it is glued in very early life, and cannot change its place. Unlike Actinia, its body is supported by a stony skeleton of calcareous plates arranged edgewise so as to radiate from the centre. But as we find some Molluscs furnished with a shell, and others even of the same character and habits without one, so we find that in spite of this seemingly important difference, the animals are very similar in their nature. Since the introduction of glass tanks we have opportunities of seeing anemones crawling up the sides, so as to exhibit their entire basal disk, and then we may observe lightly coloured lines of a less transparent substance than the interstices, radiating from the margin to the centre, some short, others reaching the entire distance, and arranged in exactly the same manner as the plates of Caryophyllæa. These are doubtless flexible walls of compartments dividing the fleshy parts of the softer animals, and corresponding with the septa of the coral. Fig. 2 _a_ represents a section of the latter, to be compared with the basal disk of Sagartia. SAGARTIA ANGUICOMA. _Pl._ V. _fig._ 3, _a_, _b_. This genus has been separated from Actinia on account of its habit of throwing out threads when irritated. Although my specimens often assumed the form represented in fig. 3, Mr. Lloyd informs me that it must have arisen from unhealthiness of condition, its usual habit being to contract into a more flattened form. When fully expanded, its transparent and lengthened tentacles present a beautiful appearance. Fig. 3 _a_, showing a basal disk, is given for the purpose already described. BALANOPHYLLÆA REGIA. _Pl._ V. _fig._ 1. Another species of British madrepore, found by Mr. Gosse at Ilfracombe, and by Mr. Kingsley at Lundy Island. It is smaller than O. Smithii, of a very bright colour, and always covers the upper part of its bony skeleton, in which the plates are differently arranged from those of the smaller species. Fig. 1 shows the tentacles expanded in an unusual degree; 1 _a_, animal contracted; 1 _b_, the coral; 1 _c_, a tentacle enlarged. PLATE VI. CORALS AND SEA ANEMONES. ACTINIA MESEMBRYANTHEMUM. _Pl._ VI. _fig._ 1 _a_.