Sethophormida et Sethophænida, Haeckel, 1881, Prodromus, p. 432, 433.
Definition.—Dicyrtida multiradiata. (Cyrtoidea with a two-jointed shell, divided by a transverse constriction into cephalis and thorax, and bearing numerous—four to nine or more—radial apophyses.)
The family Anthocyrtida, composed of the Sethophormida and Sethophænida of my Prodromus, comprises those Cyrtoidea in which the shell is two-jointed and bears numerous radial apophyses. The two subfamilies differ in the shape of the mouth, which in the Sethophormida is a simple, wide opening; in the Sethophænida closed by a lattice-plate.
Numerous fossil and living forms of Anthocyrtida were described formerly by Ehrenberg in his genera Carpocanium and Anthocyrtis. These, however, represent only a small part of the whole family, which exhibits a great variety in the composition of the lattice-work and in the number of radial beams. The number of species here described amounts to one hundred and forty, and these are disposed in fourteen genera (twelve Sethophormida and two Sethophænida).
The Sethophormida may be again divided into two different groups or tribes, the Sethamphorida and Carpocanida; in the former the thorax bears numerous radial ribs, enclosed in its wall; in the latter these ribs have disappeared, and only a corona of terminal feet is developed around the mouth. The shell of the former is usually pyramidal, with a widely open mouth; of the latter ovate, with a constricted mouth. The mouth of the thorax becomes perfectly closed in the Sethophænida.
The majority of the Anthocyrtida may be derived from the Polyspyrida (Petalospyris, &c.) by reduction of the cephalis and loss of the sagittal ring, as was suggested by Bütschli (1882, loc. cit.). But another part may also have arisen from the Tripocyrtida, by interpolation of secondary radial apophyses between the three primary perradial apophyses. The cephalis in this family is developed in all possible degrees, from one of a considerable size to one very much reduced. If it becomes perfectly lost, the Cyrtocalpida arise.
Synopsis of the Genera of Anthocyrtida.
I. Subfamily Sethophormida. Terminal mouth of the thorax a simple wide opening. |  | Radial ribs smooth (rarely thorny) enclosed in the wall of the thorax (cephalis commonly small, without horns). |  | Shell flat, campanulate or nearly discoidal (cephalis without horn), | 558. Sethophormis. | ||||
| Shell ovate, with constricted mouth (without horn), | 559. Sethamphora. | ||||||||
| Shell slender pyramidal, with straight ribs. |  | Meshes of the network simple, | 560. Sethopyramis. | ||||||
| Meshes fenestrated by secondary latticework, | 561. Plectopyramis. | ||||||||
| Meshes closed by spongy framework, | 562. Spongopyramis. | ||||||||
| Radial ribs thorny (rarely smooth) prolonged into free terminal feet (cephalis commonly large, with one or more horns). |  | Shell not enveloped by arachnoidal network, | 563. Acanthocorys. | ||||||
| Shell enveloped by arachnoidal network, | 564. Arachnocorys. | ||||||||
| No ribs in the thorax. Peristome with free terminal feet. | | Cephalis well-developed with an apical horn. |  | Feet terminal, without separate peristome. |  | Six feet, | 565. Anthocyrtoma. | ||
| Nine feet, | 566. Anthocyrtis. | ||||||||
| Twelve or more feet, | 567. Anthocyrtium. | ||||||||
| Feet subterminal, outside the constricted peristome, | 568. Anthocyrtidium. | ||||||||
| Cephalis rudimentary, hidden in the upper part of the thorax, without horn, | 569. Carpocanium. | ||||||||
II. Subfamily Sethophænida. Terminal mouth closed by a lattice-plate. | | Thorax with lateral apophyses (four to six or more wings), | 570. Sethophæna. | ||||||
| Thorax with terminal apophyses (four to six or more feet), | 571. Clistophæna. | ||||||||
I. Subfamily Sethophormida. Terminal mouth of the thorax a simple wide opening. | ||||||||||
| Radial ribs smooth (rarely thorny) enclosed in the wall of the thorax (cephalis commonly small, without horns). | ||||||||||
| Shell flat, campanulate or nearly discoidal (cephalis without horn), | ||||||||||
| 558. Sethophormis. | ||||||||||
| Shell ovate, with constricted mouth (without horn), | ||||||||||
| 559. Sethamphora. | ||||||||||
| Shell slender pyramidal, with straight ribs. | ||||||||||
| Meshes of the network simple, | ||||||||||
| 560. Sethopyramis. | ||||||||||
| Meshes fenestrated by secondary latticework, | ||||||||||
| 561. Plectopyramis. | ||||||||||
| Meshes closed by spongy framework, | ||||||||||
| 562. Spongopyramis. | ||||||||||
| Radial ribs thorny (rarely smooth) prolonged into free terminal feet (cephalis commonly large, with one or more horns). | ||||||||||
| Shell not enveloped by arachnoidal network, | ||||||||||
| 563. Acanthocorys. | ||||||||||
| Shell enveloped by arachnoidal network, | ||||||||||
| 564. Arachnocorys. | ||||||||||
| No ribs in the thorax. Peristome with free terminal feet. | ||||||||||
| Cephalis well-developed with an apical horn. | ||||||||||
| Feet terminal, without separate peristome. | ||||||||||
| Six feet, | ||||||||||
| 565. Anthocyrtoma. | ||||||||||
| Nine feet, | ||||||||||
| 566. Anthocyrtis. | ||||||||||
| Twelve or more feet, | ||||||||||
| 567. Anthocyrtium. | ||||||||||
| Feet subterminal, outside the constricted peristome, | ||||||||||
| 568. Anthocyrtidium. | ||||||||||
| Cephalis rudimentary, hidden in the upper part of the thorax, without horn, | ||||||||||
| 569. Carpocanium. | ||||||||||
II. Subfamily Sethophænida. Terminal mouth closed by a lattice-plate. | ||||||||||
| Thorax with lateral apophyses (four to six or more wings), | ||||||||||
| 570. Sethophæna. | ||||||||||
| Thorax with terminal apophyses (four to six or more feet), | ||||||||||
| 571. Clistophæna. | ||||||||||