Genus 190. Distriactis,[[229]] n. gen.
Definition.—Phacodiscida with simple medullary shell and with six radial spines on the margin of the disk placed in the equatorial plane.
The genus Distriactis exhibits on the margin of the lenticular phacoid shell six radial solid spines. Their distance is commonly equal, rarely unequal. Either all six spines are of equal size and similar form, or three larger (perradial) alternating with three smaller (interradial), so that Distriactis appears to be derived from Triactiscus by development of three secondary between three primary spines.
1. Distriactis liriantha, n. sp.
Disk smooth, four times as broad as the medullary shell, with regular, circular pores (about ten on the radius). Six marginal spines of equal size and at equal distances, triangular, sulcate, half as long as the radius. (Similar to Heliosestrum medusinum, Pl. [34], fig. 6.)
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.05; length of the spines 0.05, basal breadth 0.04.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Distriactis corallantha, n. sp.
Disk thorny, three times as broad as the medullary shell, with regular, circular pores, about eight on the radius. Six marginal spines of equal size and equidistant, conical, nearly as long as the diameter of the disk, half as broad at the base as the medullary shell.
Dimensions.—Diameter of the disk 0.12, of the medullary shell 0.04; length of the spines 0.1, breadth 0.02.