FAM. CLAVIDAE.—This is a large family containing many genera, some with free-swimming Medusae, others with adelocodonic gonophores. In the former group are included a number of oceanic Medusae of which the hydrosome stage has not yet been discovered. The zooids of the hydrosome have numerous scattered filiform tentacles. The free-swimming Medusae have hollow tentacles. _Clava_ contains a common British species with a creeping hydrorhiza frequently attached to shells, and with adelocodonic gonophores. _Cordylophora_ is the genus which has migrated into fresh water in certain European localities (see p. 269). It forms well-developed branching colonies attached to wooden gates and piers or to the brickwork banks of canals. Several Anthomedusae, of which the hydrosome stage is not known, appear to be related to the Medusae of this family, but are sometimes separated as {273}the family TIARIDAE. Of these _Tiara_, a very brightly coloured jelly-fish sometimes attaining a height of 40 mm., is found on the British coasts, and _Amphinema_ is found in considerable numbers at Plymouth in September. _Turritopsis_ is a Medusa with a hydrosome stage like _Dendroclava_. For _Stomatoca_, see p. 415. FAM. CORYMORPHIDAE.—This family contains the interesting British species _Corymorpha nutans_. The hydrosome stage consists of a solitary zooid of great size, 50-75 mm. in length, provided with two circlets of numerous long filiform tentacles. The free-swimming Medusae are produced in great numbers on the region between the two circlets of tentacles. These Medusae were formerly known by the name _Steenstrupia_, and are noteworthy in having only one long moniliform tentacle, opposite to one of the radial canals. The gigantic _Monocaulus imperator_ of Allman was obtained by the "Challenger" at the great depth of 2900 fathoms off the coast of Japan. It was nearly eight feet in length. More recently Miyajima[309] has described a specimen from 250 fathoms in the same seas which was 700 mm. (27.5 in.) in length. Miyajima's specimen resembles those described by Mark from 300 fathoms off the Pacific coast of North America as _Branchiocerianthus urceolus_ in the remarkable feature of a distinct bilateral arrangement of the circlets of tentacles. Owing to the imperfect state of preservation of the only specimen of Allman's species it is difficult to determine whether it is also bilaterally symmetrical and belongs to the same species as the specimens described by Mark and Miyajima. These deep-sea giant species, however, appear to differ from _Corymorpha_ in having adelocodonic gonophores.