Page:Scientific results HMS Challenger vol 18 part 1.djvu/542

334

Definition.—Network of the cortical shell irregular, with meshes of unequal size or dissimilar form; surface thorny or papillose.

7. Xiphatractus radiosus, Haeckel.

Stylosphæra radiosa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxiv. fig. 5.

Cortical shell very thick walled, with thorny surface, and irregular, roundish pores, once to three times as broad as the bars; nine and ten on the half equator. Polar spines conical, on the base about as broad as the largest pores; the larger as long as the main axis, the smaller scarcely one-fourth as long. (The radial striation, figured by Ehrenberg and applied to the name of this species, is produced by the contours of the funnel-shaped pores in the thick walls seen in optical section; the ellipsoidal cortical shell is double.)

Dimensions.—Major axis 0.13, minor 0.09; pores 0.003 to 0.01, bars 0.003; main axes of the two medullary shells 0.05 and 0.03; length of the major polar spine 0.12, of the minor 0.03, basal breadth 0.01.

Habitat.—Fossil in the Tertiary rocks of Barbados.

8. Xiphatractus glyptodon, n. sp. (Pl. 17, figs. 9, 10).

Cortical shell thick walled, covered with radial spines of the size of the pores; on the half equator eight to ten irregular or subregular roundish pores, twice to four times as broad as the bars. In the bottom of each pore a thin lamella of silex, perforated by four to six smaller roundish pores. Both medullary shells (fig. 10) spherical, with smaller, regular, circular pores. Larger polar spine three-sided pyramidal, in length equals the main axis; shorter spine only half as long, but twice as thick, of elegant pommel-form (fig. 9), with nine prominent edges.

Dimensions.—Major axis 0.12, minor, 0.1; pores and spines 0.01 to 0.02, bars and porules 0.005; diameter of the two medullary shells 0.05 and 0.02; length of the major polar spine 0.1, of the minor 0.06, greatest thickness 0.04.

Habitat.—Pacific, central area, Station 263, surface.

Definition.— with four or more concentric shells (two medullary shells and two or more cortical shells), in the main axis with two large opposite polar spines of equal size and similar form.

The genus Cromyatractus is very nearly allied to all the foregoing genera, which bear two equal spines opposite to one another on the poles of the main axis; it differs