Page:Scientific results HMS Challenger vol 18 part 1.djvu/671

Rh 3. Stylocyclia excavata, n. sp. (Pl. 37, fig. 8).

Phacoid shell four times as broad as the medullary shell, surrounded by four chambered rings, which are divided by twenty to thirty radial beams into broad chambers. The height of the rings increases strongly from the centre, so that the fourth ring is two and a half times as high as the first. Pores irregular, roundish; five to six on the radius of the phacoid shell, one to two on the breadth of each ring. Margin of the disk smooth. Both marginal spines thin and long, cylindrical, arising from the medullary shell, longer than the diameter of the disk.

Dimensions.—Diameter of the disk (with four rings) 0.25, of the phacoid shell 0.1, of the medullary shell 0.025.

Habitat.—Fossil in the rocks of Barbados. Indian Ocean, Cocos Islands, Rabbe.

4. Stylocyclia amphacantha, n. sp.

Phacoid shell twice as broad as the medullary shell, surrounded by five chambered rings, divided by piercing beams each into forty to fifty chambers. Pores regular, circular; eight to nine on the radius of the phacoid shell, one on each chamber. Margin of the disk thorny. Both marginal spines strong, conical, as long as its radius.

Dimensions.—Diameter of the disk (with five rings) 0.24, of the phacoid shell 0.1, of the medullary shell 0.05.

Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.

Definition.— with two opposite solid radial spines on the margin of the circular disk. Medullary shell double.

The genus Amphicyclia has the same form and structure as Stylocyclia, and differs from it only in the double concentric medullary shell. It bears therefore to the latter the same relation that Coccodiscus does to Lithocyclia.

1. Amphicyclia chronometra, n. sp. (Pl. 38, fig. 1).

Phacoid shell three times as broad as the outer and nine times as broad as the inner medullary shell, surrounded by two broad chambered rings, which are divided into irregular chambers by fifty to sixty radial beams of different distance. Margin of the disk thorny, lacerated. Pores irregular, roundish; twelve to sixteen on the radius of the phacoid shell, two to three on the breadth of each ring. The two opposite marginal spines strong, prismatic, with prominent edges, about as long as the diameter of the disk.

Dimensions.—Diameter of the disk (with two rings) 0.24, of the phacoid shell 0.15, outer medullary shell 0.05, inner 0.017.

Habitat.—Pacific, central area, Stations 265 to 268, depths 2700 to 2900 fathoms.