Page:Scientific results HMS Challenger vol 18 part 1.djvu/714

506 parallel chambered plates in the central part, and five similar plates in the peripheral part.) Pores irregular, roundish, three on the breadth of each ring. Three marginal spines long and thin, cylindrical (as in Staurodictya cruciata, Pl. 42, fig, 4), longer than the diameter of the disk, and half as thick as one ring.

Dimensions.—Diameter of the disk (with nine rings) 0.18; breadth of each ring 0.01; pores 0.002 to 0.004.

Habitat.—Pacific, central area, Station 263, depth 2650 fathoms.

Definition.— with four solid radial spines (commonly crossed at right angles) on the margin of the circular or quadrangular disk.

The genus Staurodictya is characterised by four marginal spines, lying opposite in pairs in two crossed equatorial diameters of the disk, perpendicular one to another. Sometimes the regular rectangular position of the spines becomes more or less irregular. Commonly the marginal spines are the extreme prolongations of four internal crossed radial beams, which are either rectilinear or zigzag-shaped. In the latter case the concentric disposition of the circular rings becomes more or less spiral. Perhaps Staurodictya has a near relation to the Stauralastrida (or to the Euchitonida with four crossed chambered arms—Stauralastrum, Histiastrum, &c.).

Definition.—All rings of the disk concentric (commonly circular, sometimes with four incisions, produced by two crossed constrictions, or nearly square).

1. Staurodictya medusa, n. sp. (Pl. 42, fig. 3).

All rings of the disk concentric, of nearly equal breadth, divided into four quadrants by two perradial constrictions (perpendicular one to another). Pores irregular, roundish, two to three on the breadth of each ring. Four marginal spines strong, pyramidal, nearly as long as the radius of the disk. Margin between them denticulated.

Dimensions.—Diameter of the disk (with four rings) 0.13; breadth of each ring 0.015; pores 0.002 to 0.01.

Habitat.—North Pacific, Station 244, depth 2900 fathoms.

2. Staurodictya ciliata, n. sp. (Pl. 42, fig. 2).

All rings of the disk concentric, of nearly equal breadth, circular or roundish, without perradial constrictions. Pores subregular, circular, three to four on the breadth of each ring. Four marginal