Dimensions.—Diameter of the disk 0.25, of the outer medullary shell 0.06, of the inner 0.025; pores 0.007.
Habitat.—Pacific, central area, Station 268, depth 2900 fathoms.
2. Perizona pterygota, n. sp. (Pl. [32], figs. 8, 8a).
Disk with smooth surface, six times as broad as the outer, and fifteen times as broad as the inner medullary shell. Pores regularly circular; eighteen to twenty on the radius of the disk. Margin much thickened and truncated, abruptly separated in the equatorial circumference from the peripheral sharp margin of the solid girdle; breadth of the girdle equal to that of the outer medullary shell.
Dimensions.—Diameter of the disk 0.25, of the outer medullary shell 0.04, of the inner 0.015; pores 0.006.
Habitat.—Pacific, central area, Station 266, depth 2750 fathoms.
Subfamily 2. Heliosestrida, Haeckel.
Definition.—Phacodiscida with a constant number of radial spines on the margin of the disk (two, three, four, six, or eight), which are commonly regularly disposed (sometimes more or less irregularly).
Genus 185. Sethostylus,[[224]] Haeckel, 1881, Prodromus, p. 457.
Definition.—Phacodiscida with simple medullary shell and with two radial spines on the margin of the disk, opposite in the equatorial axis.