Definition.—Distal end of the arms armed with a radial spine.
5. Trigonactura triacantha, n. sp. (Pl. [38], figs. 6, 7).
Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its radius, surrounded by one perfect chambered ring. Arms nearly lanceolate, in the middle part one and a half times as broad as at both ends, twice as long as the phacoid shell, at the distal end with a strong pyramidal terminal spine. Through the spongy framework of each arm shine sixteen to eighteen transverse bars (as septa of the joints) and six to eight longitudinal piercing beams.
Dimensions.—Diameter of the phacoid shell 0.09, of the medullary shell 0.038; length of the arms 0.2, greatest breadth 0.08.
Habitat.—Pacific, central area, Station 265, depth 2900 fathoms.
6. Trigonactura trigonodiscus, n. sp.
? Astromma sp., Bury, 1862, Polycystins of Barbados, Taf. xv. fig. 2.
Phacoid shell triangular, twice as broad as the spherical medullary shell, with six to seven pores on its radius, surrounded by one chambered ring. Arms equilateral triangular, as long as the diameter of the central disk and at the base half as broad, slowly decreasing in breadth towards the distal end, which is armed with a strong pyramidal spine.
Dimensions.—Diameter of the phacoid shell 0.1, of the medullary shell 0.05; length of the arms 0.12, basal breadth 0.07.
Habitat.—Pacific, central area, Station 268, depth 2900 fathoms; also fossil in Barbados.