Definition.—Coronida with four large, partly latticed, lateral gates, without basal gate. Skeleton composed of two meridional rings perpendicular to each other.
The genus Zygostephanium differs from the preceding ancestral genus Zygostephanus in the development of lattice-work along the two crossed rings, produced by their anastomosing branches. Therefore the four large lateral gates between them, which are quite simple, in the preceding genus here become more or less fenestrated.
1. Zygostephanium dizonium, n. sp. (Pl. [93], fig. 3).
Tympaniscus dizonius, Haeckel, 1882, Manuscript.
Both rings elliptical, of nearly equal height, smooth, without spines. Sagittal ring with four pairs of small pores (two apical pairs and two basal pairs). Frontal ring with three pairs of small pores (one pair lateral, one pair above and one pair below).
Dimensions.—Height of the frontal ring 0.08, breadth 0.12.
Habitat.—Central Pacific, Station 268, depth 2900 fathoms.
2. Zygostephanium paradictyum, n. sp. (Pl. [93], fig. 4).
Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction. Sagittal ring ovate, about two-thirds as high as the frontal ring. Both rings three-edged, armed with numerous short and branched bristle-shaped spines, which anastomose along their three edges and produce two series of irregular polygonal pores.
Dimensions.—Height of the frontal ring 0.08, breadth 0.13.