Cephalis very small, hemispherical, hyaline, without pores. Thorax flatly pyramidal, with nine concave, triangular faces and nine little curved, stout, radial beams. Between these are interpolated numerous incomplete secondary beams, which are absent in the apical part of the thorax. The radial beams being connected by numerous (thirty to forty or more) horizontal, ring-like threads, a delicate arachnoidal network with small, quadrangular pores is produced. Peristome nine-angled, with a peculiar vertical gallery, composed of four horizontal, parallel, nine-angled rings, which are connected by numerous vertical, parallel bars, therefore with three transverse rows of square pores. This peculiar species is very different from the preceding and may represent a separate genus, Craspedilium.
Dimensions.—Cephalis 0.01 diameter, thorax 0.1 long, 0.25 broad.
Habitat.—Central Pacific, Station 271, surface.
Subgenus 6. Astrophormis, Haeckel.
Definition.—Thorax with a variable number of radial ribs (twelve to twenty or more).
15. Sethophormis aurelia, n. sp. (Pl. [55], figs. 3, 4).
Leptarachnium aurelia, Haeckel, 1879, Manuscript et Atlas.
Cephalis large, nearly hemispherical, with irregular, delicate network of small square meshes. Collar-septum with four large meshes, separated by a cross of four bars, opposite in pairs. Thorax flatly campanulate, with delicate, subregular, hexagonal meshes, and twenty-four prominent radial ribs; four of these are primary or perradial (centrifugal prolongations of the four bars of the collar-septum); four others are interradial or secondary, alternating with the former at angles of 45°; sixteen others are adradial or tertiary, interpolated between the first and second more or less irregularly. In some specimens the disposition of the twenty-four ribs was more regular, in others more irregular, than in the specimen figured (figs. 3, 4). The central capsule (fig. 4) exhibits a flat, cap-shaped part with the nucleus (enclosed in the cephalis), and four large, pear-shaped lobes protruded through the four large collar holes (somewhat deformed in the preparation figured). The wall of the thorax exhibits at the base four larger, nearly semicircular pores, bisected by the four primary thoracic ribs. Peristome with twenty-four indentations (between the prominent distal ends of the twenty-four ribs), often more distinct than in the specimen figured.
Dimensions.—Cephalis 0.03 long, 0.08 broad; thorax 0.1 to 0.2 long, 0.4 to 0.6 broad.
Habitat.—Central Pacific, Station 263 to 274, depth 2350 to 2925 fathoms.