Page:Scientific results HMS Challenger vol 18 part 1.djvu/670

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

The genus Stylocyclia opens the series of the Stylocyclida or of those Coccodiscida in which the margin of the chambered disk is armed with solid radial spines, situated in its equatorial plane, but without chambered arms. Stylocyclia is the most simple form of this subfamily, and bears only two marginal spines, opposite in one equatorial axis of the disk. The medullary shell is simple. This genus corresponds to Xiphodictya in the family Porodiscida. The genus was previously known only by one single species described by Ehrenberg.

1. Stylocyclia dimidiata, Ehrenberg.

Stylocyclia dimidiata, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxix. fig. 4.

Phacoid shell three times as broad as the medullary shell, surrounded by five to eight chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square chambers. Pores subregular, circular; six to seven on the radius of the phacoid shell, a single one on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.)

Dimensions.—Diameter of the disk (with eight rings) 0.25, of the phacoid shell 0.11, of the medullary shell 0.035.

Habitat.—Fossil in the Tertiary rocks of Barbados; living in the depths of the Equatorial Atlantic, Station 348, depth (2450) fathoms.

2. Stylocyclia prionacantha, n. sp. (Pl. 37, fig. 6).

Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. Pores in the thick-walled phacoid shell regularly circular, increasing in size from the centre; eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad serrated edges.

Dimensions.—Diameter of the disk (with five rings) 0.23, of the phacoid shell 0.12, of the medullary 0.05.

Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.