Page:Scientific results HMS Challenger vol 18 part 2.djvu/359

Rh

Definition.— (vel Dicyrtida triradiata clausa), with three divergent, solid, lateral wings. Cephalis with a horn.

The genus Micromelissa differs from the two preceding genera in the free prominence of the three cortinar ribs, forming three solid lateral wings. Beyond these the thorax walls are convergent, and the basal mouth closed by a lattice-plate. Therefore Micromelissa may have arisen from Lithomelissa simply by development of this basal mouth-plate.

1. Micromelissa bombus, n. sp. (Pl. 57, fig. 14).

Shell smooth, with sharp collar stricture. Length of the two joints = 1 : 4, breadth = 1 : 5. Cephalis spherical, with an oblique conical horn of the same length. Thorax subspherical, in the upper half with three conical, downwardly diverging wings, about as long as its radius. Pores very small and scarce.

Dimensions.—Cephalis 0.02 long, 0.02 broad; thorax 0.09 long, 0.1 broad.

Habitat.—Central Pacific, Station 266, depth 2750 fathoms.

2. Micromelissa vespa, n. sp.

Shell smooth, with deep collar stricture. Length of the two joints = 2 : 5, breadth = 2 : 3. Cephalis spherical, with an oblique pyramidal horn twice the length. Thorax inversely ovate, in the upper half with three pyramidal wings, which are equal to its breadth, little curved and diverging downwards. Pores very small and scarce.

Dimensions.—Cephalis 0.04 diameter; thorax 0.1 long, 0.06 broad.

Habitat.—Western Tropical Pacific, Station 225, depth 4475 fathoms.

3. Micromelissa apis, n. sp.

Shell rough, with deep collar stricture. Length of the two joints = 2 : 3, breadth = 2 : 4. Cephalis subspherical, with a straight conical horn of half the length, and subregular, circular, double-contoured pores, of the same breadth as the bars. Thorax little larger, subspherical, with irregular, roundish pores, twice to four times as broad as the bars. From its lower half arise three short conical wings, curved downwards, and half as long as the cephalis.

Dimensions.—Cephalis 0.04 long, 0.04 broad; thorax 0.06 long, 0.08 broad.

Habitat.—South Pacific, Station 295, depth 1500 fathoms.