Page:Scientific results HMS Challenger vol 18 part 2.djvu/684

1560 centre (the apex of the pyramid). Alternating with these, three horizontal, perradial, centrifugal spines start from the base.

Dictyocha trigona, Zittel, 1876 (L. N. 29, p. 83, Taf. ii. fig. 6), is an interesting Cretaceous species, perhaps a variety of Dictyocha triommata.

Dimensions.—Diameter of the basal triangle 0.01, of the three meshes 0.005.

Habitat.—Fossil in different Tertiary deposits (of Sicily, Greece, North America); living in the Central Pacific, Stations 270 to 272, depth 2600 to 2925 fathoms.

5. Dictyocha tripyla, Ehrenberg.

Dictyocha tripyla, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

Dictyocha tripyla, Ehrenberg, 1854, Mikrogeol., Taf. xix. fig. 38 (et Taf. xxi. fig. 41?).

Each pileate piece of the skeleton is a small three-sided pyramid, similar to that of Dictyocha triommata, but differs from it in the possession of three small perpendicular teeth, which are directed downwards and start from the basal ring near the origin of the three horizontal spines.

Dimensions.—Diameter of the triangular basal ring 0.015, of the three meshes 0.007.

Habitat.—Fossil in Tertiary deposits. North Africa (Oran), Sicily (Caltanisetta).

6. Dictyocha medusa, n. sp. (Pl. 101, figs. 13, 14).

Each pileated piece of the skeleton has four equal, cruciate, triangular meshes. From the four corners of the square basal ring proceed four perradial horizontal spines, and between these four interradial curved bars, which correspond to the edges of a four-sided pyramid, arise from the centre of the four sides and become united in the centre (on the apex of the pyramid). No apical spine.

Dimensions.—Diameter of the basal ring 0.02, of the four meshes 0.01.

Habitat.—Central area of the Pacific, Station 272, depth 2600 fathoms.

7. Dictyocha staurodon, Ehrenberg.

Dictyocha staurodon, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 80.

Dictyocha staurodon, Ehrenberg, 1854, Mikrogeol., Taf. xviii. fig. 58.

Each pileated piece of the skeleton is a small, regular, four-sided pyramid, similar to the foregoing species. It differs from Dictyocha medusa in the development of a vertical apical spine, and of four small centripetal teeth, which start from the inside of the basal square, between the four perradial spines and the four ascending interradial beams.

Dimensions.—Diameter of the basal ring 0.025, of the meshes 0.01.

Habitat.—Fossil in Tertiary rocks; Tripel of Richmond, Virginia (Ehrenberg); Barbados, (Haeckel); living in the Tropical Atlantic, Station 347, surface.