All three rings equal, circular, thorny; their rods prismatic (in the transverse section triangular), with three sharp dentated edges and scattered branched thorns. From each pole of the three equal axes (which correspond to the three axes of a regular octahedron) arises a bunch of larger spines. _Dimensions._--Diameter of all three rings 0.12, thickness 0.01. _Habitat._--Central Pacific, Station 268, depth 2900 fathoms. Genus 424. _Trissocyclus_,[43] Haeckel, 1881, Prodromus, p. 446. _Definition._--#Coronida# with eight large, partly fenestrated gates of equal size. Skeleton composed of three complete latticed rings, perpendicular to one another. The genus _Trissocyclus_ differs from its nearly allied ancestral form _Trissocircus_ only in the development of small anastomosing branches along the edges of the rings. The incomplete lattice-work, produced by these anastomoses, partly protects the eight large gates. The three rings are either of equal or of different sizes. {987}Subgenus 1. _Tricyclarium_, Haeckel. _Definition._--Sagittal ring circular, smaller than the other two rings, which are both elliptical. 1. _Trissocyclus stauroporus_, n. sp. (Pl. 83, fig. 5). Sagittal ring circular, smaller than the other two equal elliptical rings. On each of the six corners (or crossing points of every two rings) are developed four small pores, forming a cross around the poles of the three axes. All three rings smooth, without spines. _Dimensions._--Height of the frontal ring 0.09, breadth 0.13. _Habitat._--Central Pacific, Station 265, depth 2900 fathoms. 2. _Trissocyclus triaxonius_, n. sp. Sagittal ring circular, smaller than the two other equal elliptical rings. From the edges of all three rings are developed small branches, which by irregular ramification and anastomoses form small irregular meshes along the rings. Similar to _Trissocircus octostoma_, but with thicker rings; it may be developed from the latter species by connection of the branches which border the rings. _Dimensions._--Height of the frontal ring 0.12, breadth 0.15. _Habitat._--South Pacific, Station 298, depth 2225 fathoms. Subgenus 2. _Tricyclonium_, Haeckel. _Definition._--All three rings equal, circular. 3. _Trissocyclus sphæridium_, n. sp. (Pl. 93, fig. 12). All three rings equal, circular, thorny; their rods prismatic, three-sided, with three denticulate edges; the teeth of the lateral edges become branched, and form by anastomoses of the branches small irregular meshes, which partly protect the eight large open gates. _Dimensions._--Diameter of the three rings 0.16, thickness 0.012. _Habitat._--Indian Ocean, Belligemma, Ceylon (Haeckel), surface Family LI. #TYMPANIDA#, Haeckel. _Parastephida_, Haeckel, 1881, Prodromus, p. 446. _Definition._--#Stephoidea# with two parallel horizontal rings, an upper mitral and a lower basal ring; both connected by complete or incomplete vertical rings, or by parallel vertical columellæ.