Page:Scientific results HMS Challenger vol 18 part 1.djvu/596

388 cortical shell very thin, with smooth surface, and very small, irregular, roundish pores; it envelops the whole internal shell at a constant distance, which equals the breadth of the square meshes. From the distal ends of the radial beams between the square meshes arise on every polar circle ten to twelve strong spines, as direct prolongations of those beams. These form two regular, polar crowns of thorns. The inner part of the thorns (between both shells) has only one-third to one-fourth the length of the outer free part. (This species represents a further development of Panicium coronatum, Pl. 40, fig. 4, by secondary formation of an external mantle, like that of Peripanartus atractus, Pl. 40, fig. 7.)

Dimensions.—Main axis 0.27, greatest breadth 0.15; pores of the internal proximal chambers 0.008 to 0.016, bars 0.004; square meshes of the distal chambers 0.03; pores of the outer cortical shell 0.003; length of the spines of the polar circles 0.1 to 0.15.

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

Definition.— with simple cortical shell and double medullary shell, with two hollow fenestrated tubes, opposite on the poles of the main axis.

The genus Panarium differs from Panartus by two hollow latticed tubes, which start from both poles of the main axis and lie in it. It repeats therefore in this family the same peculiar and remarkable formation, which we find in Pipettella among the Ellipsida, in Pipetta among the Druppulida, in Cannartidium among the Cyphinida, in Cannartus among the Artiscida, &c.

Definition.—Surface of the shell smooth, without spines or thorns.

1. Panarium facettarium, n. sp.

Surface of the cortical shell smooth. All the four chambers nearly of the same size and form, kidney-shaped, about twice as broad as long. Pores of these subregular, circular, with hexagonal frames, about as broad as the bars; nine to ten on the half meridian, twelve to fourteen on the half equator of each chamber. Polar tubuli nearly cylindrical, longer than half the main axis of the cortical shell, about one-fourth as broad as the equatorial constriction. Pores of the tubuli of the same shape as those of the chambers, but only half as large. (This species is like Pipetta tuba, Pl. 39, fig. 7, but distinguished by three parallel transverse constrictions.)

Dimensions.—Total length of the shell (without tubuli) 0.26; breadth of each chamber 0.12; pores 0.01, bars 0.01; length of the tubuli 0.15, breadth of them 0.03.

Habitat.—Pacific central area, Station 268, depth 2900 fathoms.