Synopsis of the Genera of Tripocyrtida.

I. Subfamily Sethopilida.

Terminal mouth of the thorax a simple wide opening.

A. Three radial ribs (or cortinar rods) partly or completely enclosed in the wall of the thorax. No latticed vertical cephalic wings.a. Three thoracic ribs prolonged into three terminal feet.Cephalis with a horn.Feet solid,534. Dictyophimus.
Feet latticed,535. Tripocyrtis.
No horn, feet solid,536. Sethopilium.
b. Three thoracic ribs prolonged into three lateral wings.Thorax perfectly latticed.With horn,537. Lithomelissa.
No horn,538. Psilomelissa.
Thorax with spongy framework,539. Spongomelissa.
Thorax with three large lateral holes between the three ribs,540. Clathrocanium.
c. Three thoracic ribs completely enclosed in the wall of the flat thoraxPeristome simple, smooth,541. Lamprodiscus.
Peristome with a corona of spines,542. Lampromitra.
B. Three radial ribs enclosed in the wall of the thorax and connected with the cephalic horn by three latticed vertical wings.a. Thorax completely latticedNo frontal horn (four spines),543. Callimitra.
With frontal horn (five spines),544. Clathromitra.
b. Thorax with three large lateral holes between the three ribs. No frontal horn,545. Clathrocorys.
C. Three radial beams (or cortinar rods) perfectly free, not enclosed in the wall of the thorax.Three beams outside the thorax, arising freely from the collar stricture (no cephalic hole),546. Eucecryphalus.
Three beams inside the thorax. Cephalis with a large apical hole,547. Amphiplecta.
D. Three radial terminal feet on the peristome (the three original lateral ribs are lost).Feet solid,548. Lychnocanium.
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 lateral spines.Cephalis with horn,552. Micromelissa.
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.
Three feet latticed.Shell without external mantle,556. Sethochytris.
Shell with an arachnoidal mantle,557. Clathrolychnus.
I. Subfamily Sethopilida. Terminal mouth of the thorax a simple wide opening.
A. Three radial ribs (or cortinar rods) partly or completely enclosed in the wall of the thorax. No latticed vertical cephalic wings.
a. Three thoracic ribs prolonged into three terminal feet.
Cephalis with a horn.
Feet solid,
534. Dictyophimus.
Feet latticed,
535. Tripocyrtis.
No horn, feet solid,
536. Sethopilium.
b. Three thoracic ribs prolonged into three lateral wings.
Thorax perfectly latticed.
With horn,
537. Lithomelissa.
No horn,
538. Psilomelissa.
Thorax with spongy framework,
539. Spongomelissa.
Thorax with three large lateral holes between the three ribs,
540. Clathrocanium.
c. Three thoracic ribs completely enclosed in the wall of the flat thorax
Peristome simple, smooth,
541. Lamprodiscus.
Peristome with a corona of spines,
542. Lampromitra.
B. Three radial ribs enclosed in the wall of the thorax and connected with the cephalic horn by three latticed vertical wings.
a. Thorax completely latticed
No frontal horn (four spines),
543. Callimitra.
With frontal horn (five spines),
544. Clathromitra.
b. Thorax with three large lateral holes between the three ribs. No frontal horn,
545. Clathrocorys.
C. Three radial beams (or cortinar rods) perfectly free, not enclosed in the wall of the thorax.
Three beams outside the thorax, arising freely from the collar stricture (no cephalic hole),
546. Eucecryphalus.
Three beams inside the thorax. Cephalis with a large apical hole,
547. Amphiplecta.
D. Three radial terminal feet on the peristome (the three original lateral ribs are lost).
Feet solid,
548. Lychnocanium.
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 lateral spines.
Cephalis with horn,
552. Micromelissa.
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.
Three feet latticed.
Shell without external mantle,
556. Sethochytris.
Shell with an arachnoidal mantle,
557. Clathrolychnus.

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.)