Page:Scientific results HMS Challenger vol 18 part 1.djvu/507

Rh Dimensions.—Major axis of the ellipsoid 0.14, minor axis 0.11; pores 0.012, bars 0.003; length of the polar spines 0.07, basal breadth 0.012. (Diameter of the lost medullary shell 0.03?)

Habitat.—South Atlantic, Station 338, depth 1990 fathoms.

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

The genus Ellipsostylus differs from Ellipsoxiphus only in the unequal size or different form of the polar spines, which in the former are equal. This difference does not seem important at first, but in the further development it produces very singular and strange forms. Theoretically it is always important, because the fundamental haplopolar form of the monaxon body becomes diplopolar by this differentiation.

Definition.—Network of the shell regular, with pores of equal size and similar form.

1. Ellipsostylus ornithoides, n. sp.

Proportion of the major axis of the ellipsoid to the minor = 4 : 3. Shell thin walled, with regular, circular meshes and hexagonal framework between them, like that of Xiphostylus favosus (Pl. 13, fig. 4). Circular pores about as broad as the bars; eight to nine on the half equator. Surface smooth. Polar spines three-sided pyramidal, as broad at the base as a single hexagon; the longer spine as long as the major axis, the shorter half as long.

Dimensions.—Longer axis of the ellipsoidal shell 0.16, shorter axis 0.12; pores and bars 0.006; length of the longer polar spine 0.16, of the shorter 0.08.

Habitat.—North Pacific, Station 241, depth 2300 fathoms.

2. Ellipsostylus avicularis, n. sp.

Proportion of the major axis to the minor = 3 : 2. Shell thick walled, with regular, rosette-shaped meshes, three times as broad as the bars; ten to twelve on the half equator. Every mesh on the outer margin with five to six rounded lobes, as in Xiphostylus phasianus (Pl. 13, fig. 9). Surface smooth. Polar spines sharp edged, thick; the longer straight and equal to the longer axis, the shorter half as long, shaped like a bird's head.

Dimensions.—Longer axis 0.18, shorter axis 0.12; pores 0.015, bars 0.005.

Habitat.—South Pacific, Station 300, depth 1375 fathoms.