A great number of families and genera are referred to this group, amongst which may be mentioned specially--(1) _Agalmidae_, containing the genera _Stephanomia_, _Agalma_, _Anthemodes_, _Halistemma_, &c.; (2) _Apolemidae_, with the genus _Apolemia_ and its allies; (3) _Forskaliidae_, with _Forskalia_ and allied forms; (4) _Physophoridae_, for _Physophora_ (fig. 73) and other genera, (5) _Anthophysidae_, for _Anthophysa_, _Athorybia_, &c.; and lastly the two families (6) _Rhodalidae_ and (7) _Stephalidae_ (fig. 74), constituting the group Auronectae of Haeckel. The Auronectae are peculiar deep-sea forms, little known except from Haeckel's descriptions, in which the large pneumatophore has a peculiar duct, termed the aurophore, placed on its lower side in the midst of a circle of swimming-bells. IV. CYSTOPHORIDA (_Cystonectae_, Haeckel). With a very large pneumatophore not divided into chambers, but without nectocalyces or bracts. Two sections can be distinguished, the Rhizophysina, with long tubular coenosarc-bearing ordinate cormidia, and Physalina, with compact coenosarc-bearing scattered cormidia. A type of the Rhizophysina is the genus _Rhizophysa_. The Physalina comprise the families _Physalidae_ and _Epibulidae_, of which the types are _Physalia_ (figs. 74, 75) and _Epibulia_, respectively. _Physalia_, known commonly as the Portuguese man-of-war, is remarkable for its great size, its brilliant colours, and its terrible stinging powers. BIBLIOGRAPHY.--In addition to the works cited below, see the general works cited in the article HYDROZOA, in some of which very full bibliographies will be found.