Only two genera can be recognized in this family, _Arachnoidea_, Moore, from Central Africa, and _Hislopia_, Carter, which is widely distributed in Eastern Asia. The former genus possesses an upright orificial tubule and has zooecia separated by basal tubules. Its anatomy is imperfectly known, but it certainly possesses a gizzard of similar structure to that of _Hislopia_, between which and _Victorella_ its zooecium is intermediate in form. Genus HISLOPIA, _Carter_. _Hislopia_, Carter, Ann. Nat. Hist. (3) i, p. 169 (1858). _Hislopia_, Stolickza, J. As. Soc. Bengal, xxxviii (2), p. 61 (1869). _Norodonia_, Jullien, Bull. Soc. zool. France, v, p. 77 (1880). _Hislopia_, _id._, _ibid._ x, p. 183 (1885). _Norodonia_, _id._, _ibid._ p. 180. _Echinella_, Korotneff, Biol. Centrbl. xxi, p. 311 (1901). _Hislopia_, Annandale, J. As. Soc. Bengal (new series) ii, p. 59 (1906). _Hislopia_, Loppens, Ann. Biol. lacustre, iii, p. 175 (1908). TYPE, _Hislopia lacustris_, Carter. _Zoarium._ The zoarium consists primarily of a main axis running in a straight line, with lateral branches that point forwards and outwards. Further proliferation, however, often compacts the structure into an almost uniform flat area. _Zooecia._ The zooecia (fig. 35 B, p. 190) are flat and have the orifice surrounded by a chitinous rim but not much raised above the dorsal surface. They arise directly one from another. _Polypide._ The polypide possesses from 12 to 20 tentacles. Its funiculus is rudimentary or absent. Neither the ovaries nor the testes have any fixed position on the lateral walls of the zooecium to which they are confined. The position of this genus has been misunderstood by several zoologists. Carter originally described _Hislopia_ as a cheilostome allied to _Flustra_; in 1880 Jullien perpetuated the error in describing his _Norodonia_, which was founded on dried specimens of Carter's genus; while Loppens in 1908 still regarded the two "genera" as distinct and placed them both among the cheilostomes. In 1885, however, Jullien retracted his statement that _Norodonia_ was a cheilostome and placed it, together with _Hislopia_, in a family of which he recognized the latter as the eponymic genus. Carter's mistake arose from the fact that he had only examined preserved specimens, in which the thickened rim of the orifice is strongly reminiscent of the "peristome" of certain cheilostomes, while the posterior of the four folds into which the tentacle sheath naturally falls (as in all ctenostomes, _cf._ the diagram on p. 191) is in certain conditions rather larger than the other three and suggests the "lip" characteristic of the cheilostomes. If living specimens are examined, however, it is seen at once that the posterior fold, like the two lateral folds and the anterior one, changes its form and size from time to time and has no real resemblance to a "lip."