_Actinia._—This genus contains the widely distributed and very variable species _Actinia mesembryanthemum_, one of the commonest of the Sea-anemones found in rock pools on the British coast. The colours of this species are often very beautiful (see p. 379) but variable. _Anemonia_ is a genus with remarkably long tentacles which are not completely retractile. _A. sulcata_ (sometimes called _Anthea cereus_) is very common in the rock pools of our southern coasts. _Bolocera tuediae_ is, next to _Actinoloba dianthus_, the largest of the British Anemones. It has very much the same colour as the common varieties of _Actinia mesembryanthemum_, but the body-wall is studded with minute, rounded warts. It is found between tide marks in the Clyde sea-area, but usually occurs in deeper water. FAM. 3. SAGARTIIDAE.—This family includes several genera with a contractile pedal disc, with the body-wall usually perforated by cinclides, and provided with acontia. The genera may be arranged in several sub-families distinguished by well-marked characters. Among the well-known Sea-anemones included in the family may be mentioned:— _Sagartia troglodytes_, a very common British species found in hollows in rocks. It is usually of an olive green or olive brown colour, and the upper third or two-thirds of the body-wall is beset with numerous pale suckers. _Adamsia palliata_ has a white body-wall spotted with bright red patches, and is associated with the hermit crab _Eupagurus prideauxii_. _Actinoloba_ (frequently called _Metridium_) _dianthus_ is considered the handsomest of all the British Sea-anemones. It has a lobed disc frilled with numerous small tentacles, and is uniformly coloured, creamy-white, yellow, pale pink, or olive brown. It lives well in captivity, and sometimes reaches a length of 6 inches with a diameter of 3 inches (Fig. 164). {382}_Aiptasia couchii_ is a trumpet-shaped Anemone, found under stones at low-water mark in Cornwall and the Channel Islands, with relatively slight power of retraction. _Gephyra dohrnii_ is an interesting species with twelve tentacles, which was supposed at one time to form a connecting link between the Actiniaria and the Antipathidea. It is found attached to the stems and branches of various Hydrozoa and Alcyonaria, sometimes in such numbers and so closely set that it gives the impression of having formed the substance of its support. Haddon[404] has described specimens found on the stems of _Tubularia_ from deep water off the south and south-west coasts of Ireland. It also occurs in the Mediterranean and the Bay of Biscay.