Page:Scientific results HMS Challenger vol 18 part 1.djvu/890

682 inner cortical shell is protected by an outer larger cupola, and besides this the whole shell is enveloped by a thin ellipsoidal veil (Pl. 10, fig. 15). Therefore this species may be the representative of a peculiar genus, the most highly developed of all Tholonida—Tholothauma.

1. Cubotholonium sphæroides, n. sp.

Outer cortical shell (or veil) spherical, with smooth surface; network very delicate, with very thin bars and very small irregular, roundish pores. Inner cortical shell simple, composed of six hemispherical cupolas, surrounding the six sides of the cubical central chamber, which encloses a spherical medullary shell (one-third as large as itself). Network of the inner cortical shell regular, with circular pores of the same breadth as the bars, twelve to fourteen in the basal semicircle of one cupola.

Dimensions.—Diameter of the spherical outer shell 0.2, of the inner cortical shell 0.15; pores and bars of the latter 0.006.

Habitat.—Indian Ocean, Zanzibar, Pullen, depth 2200 fathoms.

2. Cubotholonium ellipsoides, n. sp. (Pl. 10, fig. 15).

Tholothauma ellipsoides, Haeckel, 1883, MS.

Outer cortical shell (or veil) ellipsoidal, with very thin irregular network and thorny surface. Inner cortical shell double, with six double, flatly vaulted cupolas, surrounding the six sides of the Larnacilla-shaped central chamber; the double domes of each shell are in opposite pairs somewhat larger than the alternating pairs. Pores subregular, circular, about the same breadth as the bars; eight to twelve in the basal semicircle of one cupola. Central chamber with ellipsoidal medullary shell. Radial spines short, very numerous.

Dimensions.—Major axis of the outer cortical shell 0.28, minor 0.24; major axis of the inner cortical shell 0.16, minor axis 0.14; pores and bars 0.006; medullary shell 0.03.

Habitat.—Pacific, central area, Station 271, depth 2425 fathoms.

Definition.— with regular, completely latticed cortical shell, distinguished by two to four or more annular constrictions, which lie (all or partly) in the dimensive planes (sagittal, transverse, or lateral), and by which four to eight or more vaulted cupolas or dome-like chambers become separated. In the centre of this chambered cortical shell lies constantly a trizonal or Larnacilla-shaped medullary shell.

The family comprises a small number of peculiar, resembling the Tholonida in the composition of the polythalamous cortical shell by a number of cupolas or dome-shaped protuberances. But the disposition and origin of these latter