Feet latticed, 549. _Lychnodictyum_. ------------------------------------------------------------------------- II. Subfamily Sethoperida. Terminal mouth of the thorax closed by a lattice-plate. -------------------- Three divergent ribs (or cortinar rods) enclosed either in the wall or in the cavity of the thorax. ------------------------------------------------------------------------- Three ribs enclosed in the lattice-wall of the thorax, 550. _Sethopera_. Three internal rods in the cavity of the thorax, 551. _Lithopera_. ------------------------------------------------------------------------- Three divergent free lateral wings (as prolongation of the three ribs) on the sides of the thorax. ------------------------------------------------------------------------- Three solid { Cephalis with horn, 552. _Micromelissa_. lateral spines. { { No horn, 553. _Peromelissa_. Three latticed lateral wings. With horn, 554. _Sethomelissa_. ------------------------------------------------------------------------- Three free terminal feet (on the base of the thorax). ------------------------------------------------------------------------- Three feet solid, 555. _Tetrahedrina_. { Shell without external Three feet { mantle, 556. _Sethochytris_. latticed. { { Shell with an arachnoidal { mantle, 557. _Clathrolychnus_. {1195}Subfamily 1. SETHOPILIDA, Haeckel, 1881, Prodromus, p. 431. _Definition._--#Tripocyrtida#, with the basal mouth of the shell open (vel Dicyrtida triradiata aperta). Genus 534. _Dictyophimus_,[151] Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 53. _Definition._--#Sethopilida# (vel Dicyrtida triradiata aperta) with three complete thoracic ribs, prolonged into three solid divergent feet on the peristome. Cephalis with an apical horn. The genus _Dictyophimus_, comprising many common species, may be regarded as the common ancestral form of all sethopilida, and therefore also of the whole family of Dicyrtida. The cephalis bears an apical horn, and the thorax three ribs, which are prolonged over the open mouth into three solid feet. _Dictyophimus_ may be derived either from _Euscenium_ or _Peridium_ (Archiperida), or from _Tripospyris_ (Zygospyrida), or from _Plectaniscus_ (Plectanida), by development of lattice-work between the three terminal feet, which therefore become thoracic ribs. Subgenus 1. _Dictyophimium_, Haeckel. _Definition._--Shell smooth or rough, without prominent spines on the edges of the three thoracic ribs. (Commonly one single horn on the cephalis.)