Alcyonium digitatum, the commonest of the British Alcyonaria, affording a very instructive example of the general structure of that group. It lives just below the low tide line, attached to stones and shells, and growing as greyish or reddish masses, from the lobed or digitate shape of which it has acquired the popular name of "dead men's fingers." These masses, which may attain a height of ten inches, are really colonies, and. when living, one of the individual "polypes" may be seen rising from each of the white starlike spots studded over the surface. Each polype is crowned by a circle of eight fringed tentacles, in the centre of which is the mouth, leading to a digestive chamber (stomodaeum). This is open below to the body cavity, and is held in place by eight membranes known as mesenteries. The only skeletal structure present is a series of bony spicules scattered through the tissues.