3. Archidiscus trioniscus, n. sp.
Ring triangular, roundish, equilateral, connected with the central chamber by three radial beams at equal distances (120°); therefore three equal ring chambers. (Resembles the central part of the disk of Tripodictya trigonaria, Pl. 42, fig. 8, and may be the ancestral form of it.)
Dimensions.—Diameter of the ring 0.04, of the central chamber 0.014.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
4. Archidiscus trithalamus, n. sp.
Ring irregular, roundish, connected with the central chamber by three radial beams at unequal distances; therefore three ring chambers of different size. (If these differences be important, they introduce a spiral convolution in the further development of the Porodiscus arising from it.)
Dimensions.—Diameter of the ring 0.06, of the central chamber 0.016.
Habitat.—South Pacific, Station 288, surface.
Subgenus 3. Tetroniscus, Haeckel.
Definition.—Ring with four chambers, separated by four radial beams.
5. Archidiscus stauroniscus, n. sp. (Pl. 48, figs. 9, 9a).
Ring regular, square, connected with the central chamber by four radial beams at equal distances, opposite in pairs in two axes perpendicular one to another; therefore four equal ring chambers (or congruent quadrants of the ring). Resembles the central part of the disk of Staurodictya medusa, &c. (Pl. 42, figs. 1-3); also of Staurodictya gracilis, Ehrenberg, 1875 (Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxiii. fig. 3).
Dimensions.—Diameter of the ring 0.05, of the central chamber 0.016.
Habitat.—North Pacific, Station 253, depth 3125 fathoms.
6. Archidiscus tetroniscus, n. sp.
Ring elliptical, of rhomboidal fundamental form, connected with the central chamber by four radial beams, halving the sides of the rhombus and opposite in pairs in two axes which are not perpendicular one to another; therefore four ring chambers in pairs different, two opposite equal and larger than the two others.
Dimensions.—Diameter of the ring 0.05 to 0.07, of the central chamber 0.016.
Habitat.—Central Pacific, Station 263, depth 2650 fathoms.
7. Archidiscus tetrathalamus, n. sp.
Ring irregular, quadrangular, connected with the central chamber by four radial beams of increasing unequal length; therefore all four ring chambers of different size, gradually increasing
