Page:Scientific results HMS Challenger vol 18 part 1.djvu/711

Rh Dimensions.—Diameter of the disk (with three rings) 0.12; breadth of each ring 0.016; pores 0.004.

Habitat.—South Pacific, Station 302, depth 1450 fathoms.

2. Stomatodiscus osculatus, n. sp. (Pl. 48, fig. 8).

Disk elliptical, nearly twice as long as broad, with three concentric rings around the elliptical central chamber, one piercing radial beam in the main axis, the other beams interrupted. Surface of the shell with small scattered thorns. Pores very irregular, roundish, partly aggregated in groups of four to eight smaller porules. On both poles of the main axis a large elliptical marginal osculum, about as large as the central chamber, armed with a coronet of short conical spines.

Dimensions.—Length of the disk (with three rings) 0.18, breadth 0.1; pores 0.001 to 0.006.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

Definition.— with solid radial spines on the margin of the concentrically annulated disk, situated in the equatorial plane of the disk (without chambered arms and marginal oscula).

Definition.— with two opposite, solid, radial spines on the margin of the circular or elliptical disk.

The genus Xiphodictya opens the series of the Stylodictyida or of those Porodiscida in which the margin of the chambered disk is armed with solid radial spines, all situated in the equatorial plane of the disk. Xiphodictya exhibits the minimum number of spines, two being opposite on the poles of one equatorial axis of the disk. It repeats, therefore, in this family the same amphistylic formation as Sethostylus in the Phacodiscida and Stylocyclia in the Coccodiscida.

Definition.—All rings of the disk concentric, circular.

1. Xiphodictya amphibelonia, n. sp. (Pl. 42, fig. 10).

All rings of the disk concentric, circular, of equal breadth. Pores irregular, roundish, one and a half to two on the breadth of each ring. Margin of the disk thorny, of the same thickness as