Chapter I: CHONDROPHORIDA (Disconectae Haeckel, Tracheophysae Chun). With an

apical chambered pneumatophore, from which tracheal tubes may take origin (fig. 70); no nectocalyces or bracts; appendages all on the lower side of the pneumatophore arising from a compact coenosarc, and consisting of a central principal siphon, surrounded by gonosiphons, and these again by tentacles.

Three families: (1) _Discalidae_, for _Discalia_ and allied genera,
deep-sea forms not well known; (2) _Porpitidae_ for the familiar genus
_Porpita_ (fig. 69) and its allies; and (3) _Velellidae_, represented
by the well-known genus _Velella_ (figs. 70, 71), common in the
Mediterranean and other seas.