Ring regular, hexagonal, or nearly circular, connected with the central chamber by six radial beams of equal length and at equal distances (60°); therefore all six chambers of the same size and form. (Resembles the central part of the disk of Hexinastrum geryonidum, Pl. [44], fig. 4.)
Dimensions.—Diameter of the ring 0.06, of the central chamber 0.018.
Habitat.—Central Pacific, Station 271, depth 2425 fathoms.
10. Archidiscus pyloniscus, n. sp. (Pl. [48], figs. 11, 11a).
Ring triangular, connected with the central chamber by six radial beams at alternating distances; therefore three larger chambers (of looser network) alternate with three smaller chambers (of denser network); pores of the former twice to three times as large as those of the latter. This species is of peculiar importance, as an immediate transitional form to the Pylodiscida. If these three larger ring chambers lose their few lattice-beams and so became open gates, we get Triolene or Triopyle, the original forms of the Pylodiscida.
Dimensions.—Diameter of the ring 0.05, of the central chamber 0.015.
Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
11. Archidiscus hexathalamus, n. sp.
Ring irregular, roundish, or hexagonal, connected with the central chamber by six radial beams of unequal increasing length; therefore all six ring chambers of gradually increasing size (beginning a spiral convolution, original form of some Discospira).
Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.014.