Habitat.—Central Pacific, Station 266, depth 2750 fathoms.
6. Plectopyramis polygonomma, n. sp.
Shell smooth, pyramidal, very similar to the preceding species; differing from it in the irregular shape of the delicate polygonal (not tetragonal) secondary network, filling up the large rectangular meshes. The cephalis is larger, hyaline, pear-shaped, pointed, without pores, with a deep collar stricture. The nine radial beams of the thorax are less concave.
Dimensions.—Cephalis 0.04 long, 0.03 broad; thorax (with fifteen rings) 0.3 long, 0.22 broad.
Habitat.—South Pacific, Station 295, depth 1500 fathoms.
7. Plectopyramis heteromma, n. sp.
Shell smooth, slenderly pyramidal, with concave outlines. Cephalis very small, subspherical, with a small oblique, conical horn, and very small, scarce circular pores. Thorax with nine stout concavely curved radial beams, which are connected by numerous (thirty to fifty or more) interrupted transverse bars. The large irregular meshes so produced are filled up by irregular, polygonal, delicate lattice-work.
Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.6 long, 0.3 broad.
Habitat.—South Atlantic, Station 332, depth 2200 fathoms.
8. Plectopyramis serrata, n. sp.