Page:Scientific results HMS Challenger vol 18 part 2.djvu/362

1238 1. Sethomelissa hymenoptera, n. sp.

Cephalis subspherical, thorny, with a bunch of three divergent, larger apical spines. Thorax pear-shaped, with three broad, triangular, latticed wings, the superior edge of which is a horizontal, straight, and stout spine, nearly as long as the thorax. Pores irregular, roundish.

Dimensions.—Cephalis 0.03 diameter; thorax 0.11 long, 0.08 broad.

Habitat.—Central Pacific, Station 271, depth 2425 fathoms.

Definition.— (vel Dicyrtida triradiata clausa) with a three-sided pyramidal thorax, the three edges of which are prolonged into three divergent, solid, terminal feet. Cephalis with a horn.

The genus Tetrahedrina, and the two following nearly allied genera, are distinguished by the possession of three free, divergent, terminal feet, projecting over the latticed mouth of the thorax. Tetrahedrina may be derived directly from Dictyophimus, by development of a horizontal latticed mouth-plate from the middle part of the feet, the lower part of which remains free. This genus, not noticed by Ehrenberg, is similar to his Lithochytris, and common in the Barbados deposits.

1. Tetrahedrina pyramidalis, n. sp.

Shell three-sided pyramidal, smooth, with slight collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 4. Cephalis hemispherical, with small, sparsely disposed pores, and a pyramidal horn of the same length. Thorax with subregular, circular pores and three sharp edges, prolonged into three divergent pyramidal feet of the same length.

Dimensions.—Cephalis 0.03 diameter; thorax 0.12 long, 0.12 broad.

Habitat.—Fossil in Barbados.

2. Tetrahedrina pyriformis, n. sp.

Shell pear-shaped, rough, with distinct collar stricture. Length of the two joints = 2 : 6, breadth = 2 : 5. Cephalis subspherical, with a conical horn of the same length. Thorax with subregular, circular pores, ovate, at the broad base with three pyramidal, widely divergent feet of the same length. (Similar to Lychnocanium tribulus, Ehrenberg, 1875, loc. cit., pl. vii. fig. 1, but with the mouth closed by a lattice-plate.)

Dimensions.—Cephalis 0.04 diameter; thorax 0.12 long, 0.1 broad,

Habitat.—Central Pacific, Station 265, depth 2900 fathoms.