Page:Scientific results HMS Challenger vol 18 part 1.djvu/503

Rh surface spiny; between every three meshes arises a strong radial spine, twice to three times as long as the diameter of the meshes; the base of the spine is like a three-sided pyramid.

Dimensions.—Major axis of the ellipsoid 0.12, minor axis 0.08; meshes 0.006, bars 0.005.

Habitat.—Central area of the Pacific, Station 268, depth 2900 fathoms.

4. Ellipsidium opuntia, n. sp.

Proportion of the longer axis to the shorter = 5 : 4. Shell thin walled, with irregular, roundish meshes of different size and form, about twice to three times as broad as the irregular, thin bars between them; ten to fifteen meshes on the half equator. Between the meshes arise numerous thin, bristle-like, radial spines, about as long as the shorter radius of the shell. The number of the meshes may be three to four times as great as the number of the spines.

Dimensions.—Major axis of the ellipsoid 0.15, minor axis 0.12; pores 0.006 to 0.01, bars 0.003 to 0.004.

Habitat.—Southern Pacific, Station 284, surface.

5. Ellipsidium echinidium, n. sp.

Proportion of the longer axis to the shorter = 4 : 3. Shell thick walled, with irregular, roundish pores of different size and form, about as large or somewhat smaller than the broad bars; twelve to sixteen pores on the half equator. On the surface, irregularly scattered, twenty to thirty strong, three-sided pyramidal, radial spines, one-fourth to one-half as long as the main axis.

Dimensions.—Major axis of the ellipsoid 0.16, minor 0.12; pores and bars 0.002 to 0.008; length of the radial spines 0.04 to 0.08, basal breadth 0.01.

Habitat.—Equatorial Atlantic, Station 347, depth 2250 fathoms.

Definition.— with simple ellipsoidal shell, the main axis of which is prolonged at both poles into two strong opposite spines of equal size and similar form.

The genus Ellipsoxiphus was established by Dunikowski (in 1882, loc. cit.) for those simple amphistylous fenestrated shells, formerly united with Xiphosphæra, in which the mathematical form of the shell itself is not a true sphere, but an ellipsoid. It may therefore be derived from Xiphosphæra by prolongation of the axis in which lie both polar spines; but it may also be derived from Cenellipsis by the production of two equal spines at the poles of the main axis.