All rings of the disk not concentric, half spiral. Four radial beams, crossed perpendicularly and zigzag-shaped, divide each ring into four quadrants; the quarter-ring of each quadrant halves the two adjacent rings. All rings of equal breadth. Pores irregular, roundish, two on the breadth of each ring. Two opposite radial spines pyramidal, somewhat shorter than the diameter of the disk.
Dimensions.—Diameter of the disk (with six rings) 0.16; breadth of each ring: 0.014; pores 0.003 to 0.007.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
4. Xiphodictya heliospira, n. sp.
All rings of the disk not concentric, convoluted in a simple, regular, spiral line; all nearly of equal breadth. Pores subregular, circular, two on the breadth of each ring. Two opposite radial spines conical, about as long as the radius of the disk. Margin of the disk thorny. (Differs from Stylodictya heliospira, Pl. [41], fig. 8, mainly by the two strong, opposite, radial spines.)
Dimensions.—Diameter of the disk (with six rings) 0.14; breadth of each ring 0.01 to 0.012; pores 0.002 to 0.006.
Habitat.—Pacific, central area, Station 272, depth 2600 fathoms.
Genus 219. Tripodictya,[[258]] Haeckel, 1881, Prodromus, p. 460.
Definition.—Porodiscida with three solid, equidistant, radial spines on the margin of the circular or triangular disk.
The genus Tripodictya exhibits three radial spines on the margin of the disk, divergent at equal angles; rarely in some specimens the angles differ more or less. Perhaps this genus bears a near relation to the Dictyastrida (or to the Euchitonida with three chambered arms—Dictyastrum, Euchitonia, &c.).