Page:Scientific results HMS Challenger vol 18 part 2.djvu/96

972

Definition.—The two vertical rings of different heights; the frontal ring higher than the sagittal ring, therefore with a sagittal constriction in the median plane.

5. Zygostephanus reniformis, n. sp.

Frontal ring kidney-shaped, in the upper half convex, in the lower concave, in the latter with a deep sagittal constriction, armed with numerous irregular short spines. Sagittal ring thicker and lower, only two-thirds as high, with four pairs of short divergent spines (two ventral and two dorsal pairs).

Dimensions.—Height of the frontal ring 0.13, breadth 0.2.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

6. Zygostephanus violina, n. sp.

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction, armed with numerous irregular spines, which are partly simple, partly branched. Sagittal ring thicker and lower, only half as high, with a few short conical spines at the apical and basal poles.

Dimensions.—Height of the frontal ring 0.12, breadth 0.18.

Habitat.—South Atlantic, Station 332, depth 2200 fathoms.

7. Zygostephanus bicornis, n. sp. (Pl. 93, fig. 2).

Frontal ring violin-shaped, on the upper and the lower margin concave, with a deep sagittal constriction; its two halves pentagonal. Between numerous smaller spines there arise from the frontal ring six groups of larger branched spines, two odd in the corners of the highest points (curved like two horns), two branched pairs on the prominent lateral corners (at right and left), and two pairs in the corners of the lowest points (like four branched basal feet). Sagittal ring only two-thirds as high, with four pairs of irregular spines.

Dimensions.—Height of the frontal ring 0.11, breadth 0.16.

Habitat.—South Pacific Station 300, depth 1375 fathoms.

Definition.— 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.