This family includes a rather heterogeneous assembly of forms, and will probably require some rearrangement as our knowledge increases. Nearly all the species are found in the shallow waters of the tropics, and among them are to be found some of the largest Anemones of the world. _Stoichactis kenti_, from the Barrier Reef, is from one to four feet in diameter across the disc. In the West Indies these Anemones do not attain to such a great size, but _Homostichanthus anemone_ from Jamaica is sometimes 8 inches in diameter. FAM. 3. RHODACTIDAE.—In this family the body-wall is smooth and the oral disc greatly expanded. The tentacles are of two kinds. On the margin there is a single cycle of minute tentacles, while on the disc there are numerous tuberculate or lobed tentacles. Many of the species of this family are quite small, but _Actinotryx mussoides_ from Thursday Island has an oral disc 8 inches in diameter. The genera and species are widely distributed in the warm, shallow waters of the world. FAM. 4. THALASSIANTHIDAE.—The tentacles are simple or {384}ramified (Fig. 166), and in some cases very long (_Actinodendron arboreum_). Many of the specimens of _A. plumosum_ and _Megalactis griffithsi_ are of very large size, 8 to 12 inches in diameter. Of the former of these two species Saville Kent remarks: "The colours are lacking in brilliancy, being chiefly represented by varying shades of light brown and white, which are probably conducive to its advantage by assimilating it to the tint of its sandy bed. When fully extended the compound tentacles are elevated to a height of 8 or 10 inches, and bear a remarkable resemblance to certain of the delicately branching, light brown sea-weeds that abound in its vicinity." The same author calls attention to their stinging, which is "nearly as powerful as the ordinary stinging nettle." [Illustration: FIG. 166.—_Actinodendron plumosum._ _D_, disc of attachment; _Si_, siphonoglyph; _t_, _t_, lobes of the marginal disc bearing the tentacles; _W_, body-wall. Height of the column 200 mm. (After Haddon.)] ORDER III. MADREPORARIA.