Page:Scientific results HMS Challenger vol 18 part 2.djvu/332

1208 14. Lithomelissa decacantha, n. sp. (Pl. 56, fig. 2).

Sethomelissa decacantha, Haeckel, 1881, Prodromus et Atlas.

Shell smooth, with deep collar stricture, and with ten prismatic spines of nearly equal size and similar form. Relative length and breadth of the two joints about equal. Cephalis ovate, in the upper half hyaline, in the lower half with few scattered pores; in the equator with four prismatic horns of the same length, which diverge upwards; three of them are placed in the same meridional planes as the three wings and the three feet of the thorax (one occipital and two parietal); the fourth (frontal) horn is opposed to the occipital. Thorax campanulate, three-edged, with three vertical prominent feet (directed downward) and three horizontal wings, arising from their knees. Mouth wide open, not constricted.

Dimensions.—Cephalis 0.05 diameter; thorax 0.05 long, 0.06 broad.

Habitat.—Equatorial Atlantic, Station 347, surface.

Definition.— (vel Dicyrtida triradiata aperta) with three free lateral wings, or solid spines arising from the sides of the thorax. No terminal feet. Cephalis smooth, without a horn.

The genus Psilomelissa has the same formation of the shell as the nearly allied preceding genus Lithomelissa, and may be derived from it by reduction and loss of the cephalic horn. The cephalis is quite bare.

1. Psilomelissa galeata, Haeckel.

Dictyocephalus galeatus, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, Taf. vii. fig. 25.

Shell smooth, with sharp collar stricture. Relative length of the two joints = 5 : 3, breadth = 4 : 5. Cephalis ovate, with numerous irregular, roundish pores. Thorax truncate, conical, with a few small pores. From its upper part (below the collar stricture) there arise three thin, bristle-shaped, widely divergent wings, about as long as the cephalis. Mouth widely open.

Dimensions.—Cephalis 0.05 long, 0.04 broad; thorax 0.03 long, 0.05 broad.

Habitat.—Western Tropical Pacific, Stations 200 to 225, surface.

2. Psilomelissa phalacra, n. sp.

Shell smooth, with deep collar stricture. Relative length of the two joints = 5 : 6, breadth = 4 : 4. Cephalis ovate, hyaline, with few small pores only in the lower third. Thorax cylindrical, truncate, with small irregular, roundish pores. From its upper third there arise below the stricture three