Page:Scientific results HMS Challenger vol 18 part 2.djvu/842

1718 marginal pores small, nearly circular; the dorsal and ventral pores oblongish-hexagonal, twice as long as broad, about four to six times as long as the bars, regularly arranged in transverse rows.

Dimensions.—Length of the shell 0.22, height 0.21, breadth 0.2.

Habitat.—Tropical Atlantic, near Sierra Leone, Station 348, depth 2450 fathoms.

4. Concharium bacillarium, n. sp. (Pl. 123, fig. 4).

Shell walnut-shaped, with panelled surface; oral and aboral face of the same form. Its longitudinal diameter about one-fifth longer than the two other diameters. Borders of the two cup-shaped valves elliptical, smooth, with a prominent edge, about as broad as the larger pores. In the half frontal perimeter of the shell fifty to fifty-five pores, in the half sagittal perimeter thirty-six to forty, in the half equator also thirty to forty. Pores hexagonally framed. The pores are tapering in size from the sagittal plane towards the valve-margins, and so regularly arranged in meridional rows that the crests between the latter converge towards both poles of the longitudinal axis.

Dimensions.—Length of the shell 0.2, height 0.15, breadth 0.15.

Habitat.—Tropical Atlantic, off St. Helena, Station 340, depth 1500 fathoms.

5. Concharium fragilissimum, n. sp.

Shell subspherical, very thin-walled and fragile. Diameter in all directions nearly the same. Oral and aboral face scarcely different. Margins of the hemispherical valves extremely thin and hyaline. Pores irregularly roundish, of very different sizes and unequal forms. The fragile shell of this species differs in general shape from that of all other Concharida, and is like that of the Cœlodendrida (Pl. 121, fig. 3), but exhibits neither an apical cupola or galea, nor radial tubes arising from it. It may be perhaps a young specimen of Cœlodendrum.

Dimensions.—Diameter of the shell 0.22, of the pores 0.002 to 0.02.

Habitat.—Mediterranean, Portofino (Haeckel), surface.

Definition.— with the lateral margins of the valves smooth, without sagittal keel, but with two caudal horns on the hinge (a dorsal and a ventral).

The genus Conchasma is closely allied to the preceding Concharium, and has the same hemispherical valves with smooth margins, without teeth; but it differs from the latter in the development of two caudal horns or posterior spines on the aboral hinge, one horn on the aboral end of each valve. The three species of this genus were all found in great depths of the Antarctic Ocean, in Diatom ooze, between 1260 and 1975 fathoms, at Stations 152 to 157.