Page:Scientific results HMS Challenger vol 18 part 2.djvu/434

1310

Definition.— (vel Dicyrtida eradiata clausa) with a free cephalis bearing an apical horn.

The genus Sethocapsa and the two following genera represent together the small subfamily of Sethocapsida, or those Dicyrtida in which the mouth of the thorax is closed, and no radial apophyses are present. Sethocapsa may be derived either from Lithopera by loss of the three radial rods, or from Sethocyrtis by closure of the mouth.

1. Sethocapsa pyriformis, n. sp. (Pl. 57, fig. 2).

Shell rough, pear-shaped, with slight collar stricture. Length of the two joints = 3 : 10, breadth = 3 : 8. Cephalis subspherical, with numerous small pores, and a short pyramidal or conical horn of half the length. Thorax ovate, with subregular, circular, quincuncial pores.

Dimensions.—Cephalis 0.03 diameter, thorax 0.1 long, 0.08 broad.

Habitat.—Central Pacific, Stations 263 to 274, depth 2350 to 3000 fathoms.

2. Sethocapsa lagena, Haeckel.

Lithopera lagena, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 78, Taf. iii. fig. 4.

Shell smooth, pear-shaped, with sharp collar stricture. Length of the two joints = 3 : 8, breadth = 3 : 6. Cephalis pear-shaped, with few scarce pores, and a small conical horn of half the length. Thorax pear-shaped, with irregular, roundish pores. This species differs from the similar Lithopera lagena almost only in the complete absence of the three internal radial collar beams inside the thorax, and may be derived from it by their retrograde metamorphosis.

Dimensions.—Cephalis 0.03 diameter, thorax 0.08 long, 0.06 broad.

Habitat.—Fossil in Barbados.

3. Sethocapsa macroceros, n. sp.

Shell smooth, pear-shaped, with slight collar stricture. Length of the two joints = 2 : 11, breadth = 2 : 9. Cephalis subspherical, with small circular pores, and a very large, straight, pyramidal horn, of about the same length as the shell. Thorax ovate, with large, irregular, roundish pores, which are surrounded by polygonal frames.

Dimensions.—Cephalis 0.02 diameter, thorax 0.11 long, 0.09 broad.

Habitat.—Central Pacific, Station 270, depth 2925 fathoms.