Subgenus 2. Hexonaspidium, Haeckel.
Definition.—Six hydrotomical spines of unequal size, two opposite (equatorial) much larger than the four other (polar) spines.
4. Hexonaspis hastata, n. sp. (Pl. [140], fig. 16).
Six hydrotomical spines of unequal size; two larger equatorial spines with six prominent wings, about as long as the radius of the shell and half as broad at the base; the four polar spines quite as broad, but only half as long, nearly equilateral triangular, with two shallow furrows on each flat side at the broader base. The fourteen smaller spines not visible on the surface, quite rudimentary. Crests of the surface elegantly denticulated.
Dimensions.—Diameter of the shell 0.14; length of the two equatorial spines 0.08, of the four polar spines 0.04; basal breadth 0.04.
Habitat.—Central Pacific, Station 271, surface.
Genus 379. Hexacolpus,[[419]] n. gen.
Definition.—Hexalaspida with six prominent radial spines (in the hydrotomical plane), which are surrounded by prominent sheaths at the base; the fourteen other spines quite rudimentary, not prominent.
The genus Hexacolpus differs from the preceding Hexonaspis in the development of conical or cylindrical sheaths around the basal parts of the radial spines. It bears to the latter the same relation as Hexaconus exhibits to Hexalaspis.