Page:Scientific results HMS Challenger vol 18 part 1.djvu/531

Rh Dimensions.—Longer axis of the outer shell 0.1 to 0.15, shorter axis 0.05 to 0.12; pores 0.018 to 0.024, bars 0.002 to 0.004; diameter of the inner shell 0.04 to 0.08; length of the polar spines 0.08 to 0.2, basal thickness 0.01 to 0.02.

Habitat.—Central area of the Pacific, common; Stations 266 to 272, depth 2425 to 2900 fathoms; also fossil in Barbados.

12. Lithatractus jugatus, n. sp. (Pl. 16, fig. 2).

Stylosphæra jugata, Haeckel, 1881, Prodromus et Atlas (pl. xvi. fig. 2).

Outer shell thick walled, smooth, or somewhat reticulated, with a peculiar, irregular, double network. The pores are roundish, of very different sizes, with double margin of the outer aperture, and so irregularly distributed in polygonal groups that every group contains two to six pores immediately touching each other; the groups are separated by broader bars. On the half equator of the shell are about six to eight groups and twelve to eighteen pores. Proportion of the longer axis of the ellipsoidal shell to the shorter = 6 : 5 or 5 : 4. Inner ellipsoidal shell about half the size; its pores are not easy to make out. Polar spines three-sided pyramidal, with prominent edges, about half as long as the major axis, as broad at the base as a group of pores. (Nearly allied to Stylosphæra jugata, p. 137.)

Dimensions.—Longer axis of the cortical shell 0.12 to 0.16, shorter axis 0.1 to 0.13; pores 0.01 to 0.02; length of the polar spines 0.06 to 0.08, basal breadth 0.03 to 0.4.

Habitat.—Central area of the Pacific, Stations 266 to 272, depth 2425 to 2900 fathoms.

Definition.—Network of the outer shell irregular, with meshes of unequal size or dissimilar form; surface thorny or papillose, covered with small conical spines or tubercles.

13. Lithatractus conostylus, n. sp.

Outer shell thorny, thin walled, with irregular network; pores roundish, of unequal size, twice to four times as broad as the thin bars; sixteen to twenty on the half equator. Proportion of the longer axis to the shorter = 5 : 4. Shorter axis twice the diameter of the inner spherical shell. Polar spines conical, very stout, longer than the main axis, its base equals one-third of the minor axis.

Dimensions.—Major axis of the cortical shell 0.1, shorter axis 0.08; pores 0.004 to 0.002, bars 0.001; diameter of the medullary shell 0.04; polar spines—length 0.12, thickness 0.03.

Habitat.—Central area of the Pacific, Station 271, depth 2425 fathoms.

14. Lithatractus gamoporus, n. sp.

Outer shell thorny, thick walled, with irregular network; pores roundish, of unequal size, so irregularly distributed in polygonal groups that in every group two to six pores (commonly three to four) are near together; the groups are separated by broader bars. On the half equator