Page:Scientific results HMS Challenger vol 18 part 1.djvu/539

Rh

Definition.—Network of the outer shell irregular, with meshes of different size and form; surface thorny or papillose, covered with small spinules or tubercles.

8. Stylatractus papillosus, n. sp.

Cortical shell thin walled, with papillose surface, and irregular, simple, roundish pores, ten to sixteen on the half equator, twice to three times as broad as the bars. Conical papillæ of the surface irregularly scattered. Polar spines conical, about as long as the main axis, at the base half as broad as the inner medullary shell.

Dimensions.—Major axis 0.12, minor 0.1; pores 0.006 to 0.01, bars 0.003; main axes of the medullary shells 0.09 and 0.06; length of the polar spines 0.13, basal breadth 0.04.

Habitat.—Indian Ocean, surface (between Socotra and Ceylon), Haeckel.

9. Stylatractus disetanius, n. sp.

Cortical shell thin walled, with spiny surface, and irregular, roundish pores, eight to ten on the half equator, twice to three times as broad as the bars. Every pore is divided by thinner bars into four to six small roundish porules. Polar spines three-sided pyramidal, nearly as long as the main axis, as broad at the base as the inner medullary shell. (Resembles Xiphatractus glyptodon, Pl. 17, figs. 9, 10, but differs from it by the irregular network and the equal size of both polar spines.)

Dimensions.—Major axis 0.14, minor 0.1; pores 0.02, bars 0.008, porules 0.007; main axes of the two medullary shells 0.08 and 0.05; length of the polar spines 0.13, basal breadth 0.04.

Habitat.—South Pacific, near New Zealand, Station 169, surface.

Definition.— with a simple ellipsoidal cortical shell and double medullary shell, in the main axis with two large opposite polar spines of different size or form.

The genus Xiphatractus differs from the nearly related Stylatractus in the differentiation of two polar spines (in the same manner as Druppatractus differs from Lithatractus). From the spherical Amphistylus it differs in the ellipsoidal form of the cortical shell.

Definition.—Network of the cortical shell regular or subregular, with meshes of nearly equal size and similar form; surface smooth, without thorns or papillæ.