Habitat.—South Atlantic, Station 342, depth 1445 fathoms.
Genus 422. Tricyclidium,[[41]] Haeckel, 1881, Prodromus, p. 446.
Definition.—Coronida with eight large, partly fenestrated gates; the four upper or lateral gates larger than the four lower or basal gates. Skeleton composed of three latticed complete rings, perpendicular to one another.
The genus Tricyclidium differs from the preceding Tristephanium, its ancestral form, in the development of loose rudimentary lattice-work along the rings, and therefore bears to it the same relation that Plectocoronis does to Eucoronis. It may pass directly over into Dictyospyris.
1. Tricyclidium dictyospyris, n. sp. (Pl. [93], fig. 13).
Sagittal ring ovate, twice as thick as the two other larger rings, which become very thin, thread-like at the lateral junction, and are both slightly violin-shaped, in the middle sagittal plane constricted; the frontal ring larger than the basal. All three rings bear small scattered spines, which are irregularly branched, and by anastomoses of the thread-like branches form small irregular meshes along the rings. The four basal gates are of equal size.
Dimensions.—Height of the frontal ring 0.11, breadth 0.15.
Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.
2. Tricyclidium semantrum, n. sp.
Sagittal ring ovate, smaller than the violin-shaped frontal ring and larger than the elliptical basal ring. All three rings of nearly equal thickness, armed with short irregular branches, which are partly connected, and forming small irregular meshes along the rings. The four basal gates are of different sizes; the two anterior (jugular) gates only half as large as the two posterior (cardinal) gates.