Page:Scientific results HMS Challenger vol 18 part 2.djvu/681

Rh 9. Mesocena octogona, Ehrenberg.

Mesocena octogona, Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 417, Taf. i., Nr. iii. fig. 27.

? Mesocena heptagona, Ehrenberg, 1841, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 417, Taf. i., Nr. iii. fig. 26.

? Mesocena heptagona, Ehrenberg, 1854, Mikrogeol., Taf. xx. fig. 49.

? Mesocena octoradiata, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

? Mesocena nonaria, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, pp. 163, 273.

Rings regular, octagonal, with eight radial spines on the eight corners of the ring (sometimes between the common octoradiate rings single rings with seven or nine teeth are intermingled in one and the same calymma).

Dimensions.—Diameter of the rings 0.02, length of the spines 0.005.

Habitat.—Tropical Pacific; Peru, Ehrenberg; Station 272 to 274, surface.

10. Mesocena bisoctona, Ehrenberg.

Mesocena bisoctona, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 78; Mikrogeol., Taf. xxxv., Nr. xviii. figs. 9, 10.

Mesocena binonaria, Ehrenberg, 1845, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 78, ''loc. cit.''

Rings circular, with sixteen teeth; eight stronger teeth regularly disposed on the outer margin, alternating with these eight smaller teeth on the inner margin.

Dimensions.—Diameter of the rings 0.02, length of the outer spines 0.005.

Habitat.—Fossil in Guano from Peru and South Africa, also in Barbados.

11. Mesocena stellata, n. sp. (Pl. 101, fig. 9).

Rings circular, with sixteen teeth regularly disposed on the outer margin of the rings, eight stronger teeth alternating with eight smaller.

Dimensions.—Diameter of the rings 0.03, length of the larger spines 0.01.

Habitat.—Central area of the Pacific, Station 270, depth 2925 fathoms.

Definition.— with a skeleton composed of annular pieces, which are fenestrated by one or more arches, arising on one side of the simple ring, but do not form a truncated pyramid (therefore no apical ring).

The genus Dictyocha is a very remarkable and interesting form of, which has had a curious history. Ehrenberg, who first observed single pieces of it fossil in Tertiary rocks, supposed it to be the siliceous carapace of a Diatom, and gave it the following