Page:Scientific results HMS Challenger vol 18 part 2.djvu/764

1640 The central capsule of the Cannosphærida is small (of 0.1 to 0.15 in diameter) and hidden in the aboral half of the enclosing inner shell, whilst the oral half of the latter is filled up by the phæodium (figs. 2, 4). The structure of the capsule and of its three openings seems to be the same as in the closely allied Aulosphærida. I have, however, not been able to recognise the two parapylæ or secondary openings, and have only observed the astropyle or the main-opening with its radiate operculum surrounded by the phæodium, and directed with its tubular proboscis towards the mouth of the inner shell. As R. Hertwig also could not recognise the two parapylæ, it is not impossible that they are wanting, and that the Cannosphærida possess only one opening, the astropyle, like the Medusettida and Challengerida. The nucleus, enclosed in the central capsule, is spherical, half or one-third as broad as the latter, and contains numerous nucleoli.

Definition.— with a solid, not latticed internal shell.

The genus Cannosphæra comprises those Cannosphærida in which the inner shell is formed by a thin solid siliceous-plate and exhibits no pores between the prominent bases of the radial beams.

1. Cannosphæra atlantica, n. sp. (Pl. 112, figs. 5, 6).

Internal shell not mammillate, with fifteen to twenty radial rods, which are loosely studded with single, scattered, simple, lateral spines. External shell with irregular, mostly hexagonal meshes, armed with numerous scattered forks of paired divergent spines, and with twenty to thirty larger simple radial spines, which are about half as long as the internal rods, and bear at the distal end a verticil of three to five curved, simple, terminal branches.

Dimensions.—Diameter of the inner shell 0.1, of the outer 0.5.

Habitat.—Tropical Atlantic, Stations 347 to 349, depth 2250 to 2450 fathoms.

2. Cannosphæra antarctica, n. sp. (Pl. 112, figs. 1-3).

Internal shell mammillate, with sixty to ninety radial rods, which are studded with cruciate verticils of tridentate anchor-threads. External shell with irregular, mostly pentagonal meshes,