3. Sethostaurus rhombostaurus, n. sp. (Pl. 31, fig. 4).
Disk with smooth surface, two and a half times as broad as the medullary shell. Pores regular, circular; ten to eleven on the radius. Margin simple, smooth, without girdle. Two opposite spines longer than the diameter of the disk, four times as long as the two others, which only equal its radius. Spines sword-shaped, angular.
Dimensions.—Diameter of the disk 0.14, of the medullary shell 0.06; length of the major spines 0.2, of the minor 0.05, breadth 0.025.
Habitat.—North Atlantic, Station 353, depth 2965 fathoms.
4. Sethostaurus recurvatus, n. sp. (Pl. 31, fig. 3).
Disk with smooth surface, three times as broad as the medullary shell. Pores irregular, roundish; eight to nine on the radius. Margin simple, smooth, without girdle. Four spines cylindrical, irregularly curved, of different sizes; one single very large, much longer than the three others; two opposite lateral spines recurved, hook-shaped.
Dimensions.—Diameter of the disk 0.15, of the medullary shell 0.05; length of the major spine 0.32, of the opposite spine 0.16, of both lateral spines 0.08.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
Subgenus 2. Heliostaurus, Haeckel 1881, Prodromus, p. 457.
Definition.—Margin of the disk with a solid equatorial girdle or a corona of spines.
5. Sethostaurus cruciatus, n. sp. (Pl. 31, fig. 5).
Disk with smooth surface, three times as broad as the medullary shell. Pores regular, circular; eleven to twelve on the radius. Margin with a solid, radially striped girdle, which bears on the periphery forty to fifty triangular pointed teeth of unequal length. Four crossed spines of equal size and similar form, pyramidal, sulcated, about as long as the radius of the disk, as broad at the base as the girdle.
Dimensions.—Diameter of the disk 0.2, of the medullary shell 0.06; length of the crossed spines 0.1, basal breadth 0.02.
Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.
6. Sethostaurus coronatus, n. sp.
Disk with spiny surface, twice as broad as the medullary shell. Pores irregular, roundish; nine to ten on the radius. Margin of the disk with a solid broad girdle, bearing on the periphery a corona of thirty to forty flat tongue-shaped teeth of different length. Four crossed spines
