The genus Clistophæna agrees with the preceding Sethophæna in the mouth of the thorax being closed by a lattice-plate. But the appendages of the thorax are terminal feet, not lateral wings; their number is commonly six or nine, rarely more. Clistophæna may be derived either from Tetrahedrina by interpolation of secondary feet between the three primary, or from Sethamphora by development of a basal lattice-plate closing the mouth.
1. Clistophæna rüstiana, n. sp. (Pl. 57, fig. 6).
Shell rough, with distinct collar stricture. Length of the two joints = 3 : 10, breadth = 4 : 11. Cephalis hemispherical, with small, circular pores and a stout oblique horn three times the length, which is three-sided prismatic, and at the top denticulate. Thorax subconical, inflate, with regular, circular, quincuncial pores, increasing in size towards the base. Margin of the flat base, with six divergent, stout feet of the same prismatic form as the cephalic horn, with denticulate distal ends, about as long as the thorax. This elegant species is dedicated to Dr. Rüst of Freiburg, the discoverer of numerous fossil Radiolaria in the Liassic and Jurassic formations.
Dimensions.—Cephalis 0.03 long, 0.04 broad; thorax 0.1 long, 0.11 broad.
Habitat.—Central Pacific, Station 265, depth 2900 fathoms.
2. Clistophæna hexolena, n. sp.
Shell smooth, with slight collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 5. Cephalis subspherical, small, with a large, vertical, cylindrical horn, about as long as the shell, and small, circular pores. Thorax nearly three-sided pyramidal or tetrahedral, with three rounded edges and sub-regular, circular pores. Margin of the flat base with six conical, divergent, straight feet, somewhat shorter than the thorax. (Three on the corners, one on the middle of each side of the triangular base.)
Dimensions.—Cephalis 0.03 diameter, thorax 0.12 long, 0.14 broad.
Habitat.—North Pacific, Station 241, depth 2300 fathoms.
3. Clistophæna pyramidalis, n. sp.
Shell smooth, with slight collar stricture. Length of the two joints = 2 : 8, breadth = 3 : 10. Cephalis hemispherical, with a stout pyramidal horn of twice the length. Thorax six-sided pyramidal, with regular, circular pores of equal size, and six prominent, straight edges, which are prolonged into six divergent, pyramidal feet of half the length.
Dimensions.—Cephalis 0.02 long, 0.03 broad; thorax 0.08 long, 0.1 broad.
Habitat.—Central Pacific, Station 274, depth 2750 fathoms.
