Page:Scientific results HMS Challenger vol 18 part 1.djvu/532

324 six to eight groups and eighteen to twenty-four pores. Proportion of the longer axis to the shorter = 6 : 5. Shorter axis equals twice the diameter of the inner ellipsoidal shell. Polar spines three-sided pyramidal, about as long as the equatorial axis, as broad at the base as a group of pores.

Dimensions.—Major axis of the cortical shell 0.12, minor axis 0.1; pores 0.004 to 0.012, bars 0.003; length of the polar spines 0.1, basal breadth 0.03.

Habitat.—Central area of the Pacific, Stations 271 to 274, depth 2350 to 2750 fathoms.

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

The genus Druppatractus differs from its near relation Lithatractus in the differentiation of the two polar spines, which are different in size or form, often to a very considerable degree. It has therefore the same relation to the latter that Ellipsoxiphus bears to Ellipsostylus.

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

1. Druppatractus ichthydium, n. sp.

Cortical shell thin walled, with smooth surface and regular network. Proportion of the major axis to the minor = 3 : 2. Pores circular, hexagonally framed, twice as broad as the bars; seven to eight on the half equator (as in Xiphostylus alcedo, Pl. 13, fig. 4). Medullary shell spherical, one-third as broad as the cortical shell. Polar spines straight, three-sided pyramidal, as broad at the base as one mesh; the longer equals the main axis of the cortical shell, the shorter only its half.

Dimensions.—Major axis of the ellipsoidal cortical shell 0.18, minor axis 0.12; pores 0.01, bars 0.005; diameter of the medullary shell 0.04; length of the major polar spine 0.16 to 0.2, of the minor 0.01 to 0.12, basal breadth 0.01.

Habitat.—Mediterranean (Corfu), surface, Haeckel.

2. Druppatractus hippocampus, n. sp. (Pl. 16, figs. 10, 11).

Stylosphæra hippocampus, Haeckel, 1881, Atlas, pl. xvi. figs. 10, 11.

Cortical shell thick walled, with smooth surface and regular network. Proportion of both axes = 7 : 6. Pores circular, hexagonally lobed, three times as broad as the bars; nine to ten on the half