Page:Scientific results HMS Challenger vol 18 part 1.djvu/843

Rh central chamber, is the transverse girdle (the single girdle of Monozonium). On the poles of its major axis (the transverse axis) it is connected with the larger girdle, the elliptical perimeter of which circumscribes the lateral plane. The minor axis of this latter is the major axis of the former. Between the two crossed girdles remain four larger openings or gates, quite as in Tetrapyle. But whilst in Tetrapyle the enclosed medullary shell is a trizonal Larnacilla-shell, here in Dizonium it is a simple spherical or lentelliptical chamber.

Definition.—Shell smooth or rough, without radial spines or thorns.

1. Dizonium circulare, n. sp.

Central chamber of the shell spherical, smooth, with four to five pores on the half equator. Lateral girdle circular, three times as broad as the former. Four gates semilunar, twice as broad as high. No radial spines.

Dimensions.—Diameter of the central chamber 0.02, of the lateral girdle 0.06; height of the gates 0.02, breadth 0.04.

Habitat.—Pacific, central area, Station 274, surface.

2. Dizonium ellipticum, n. sp.

Central chamber of the shell elliptical, smooth, with three to four pores on the half equator. Lateral girdle elliptical, three times as long and broad as the central chamber. Four gates kidney-shaped, twice as broad as high. No radial spines.

Dimensions.—Length of the central chamber 0.03, breadth 0.02; length of the lateral girdle 0.09, breadth 0.06; height of the gates 0.02, breadth 0.038.

Habitat.—South Pacific, Station 288, surface.

3. Dizonium transversum, n. sp.

Central chamber of the shell spherical, rough, with five to six pores on the half equator. Lateral girdle transverse-elliptical, so that its longer axis corresponds to the lateral axis of the transverse girdle, and equals four times the diameter of the central chamber. Four gates kidney-shaped, four times as broad as high. No radial spines.

Dimensions.—Diameter of the central chamber 0.02; length of the lateral girdle 0.05, breadth 0.08; height of the gates 0.01, breadth 0.04.

Habitat.—Pacific, central area, Station 274, depth 2750 fathoms.