Page:Scientific results HMS Challenger vol 18 part 2.djvu/690

1566 9. Distephanus sirius, Haeckel.

Actiniscus sirius, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 68.

Dictyocha sirius, Ehrenberg, 1854, Mikrogeol., Taf. xviii. fig. 59.

Each pileated piece of the skeleton is a truncated six-sided pyramid, similar to that of Distephanus speculum, but distinguished by the six broad, triangular, peripheral spines, which are articulated and connected by a thin siliceous membrane (like a web-membrane); each spine has three articulations (as in Dictyocha pentasterias).

Dimensions.—Diameter of the basal ring 0.02, of the apical ring 0.005.

Habitat.—Fossil in Tertiary rocks (Richmond, Virginia), but also living in the Atlantic Ocean, Gulf Stream, Færöe Channel, John Murray, 1880.

10. Distephanus corona, n. sp. (Pl. 114, figs. 7-9).

Dictyocha corona, Haeckel, 1881, Prodromus.

Each pileated piece of the skeleton is a truncate six-sided pyramid like that of Distephanus speculum, but differing in the number (twenty-four) of teeth or spines. Six interradial ascending beams connect the two horizontal rings between these, and six nearly vertical spines arise from the perradial corners of the upper hexagonal ring. In the same meridional (perradial) plains six larger spines descend downwards from the corners of the lower larger ring. Between these six descending spines and the six ascending beams arise from the upper edge of the lower ring twelve shorter teeth of unequal size (the right tooth in each pentagonal lateral mesh being smaller and directed upwards, the left tooth being larger and directed nearly horizontally outwards). The lower ring is nearly dodecagonal.

Dimensions.—Diameter of the basal ring 0.025 to 0.03, of the apical ring 0.012 to 0.02.

Habitat.—North-west Pacific, Sea of Japan, Station 231, depth 2250 fathoms.

11. Distephanus octonarius, Haeckel.

Dictyocha octonaria, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 201.

Dictyocha polyactis, Ehrenberg, 1844, ''loc. cit.'', p. 80; Mikrogeol., 1854, Taf. xxii. fig. 50.

Dictyocha septenaria, Ehrenberg, 1844, ''loc. cit.'', p. 80; Mikrogeol., 1854, Taf. xxi. fig. 45.

Each pileate piece of the skeleton is a truncated eight-sided pyramid, composed of two regular octagonal rings, which lie in parallel plains, and are connected by eight radial beams. From the eight outer corners of the lower ring (or from the eight interradial meshes, between the eight perradial beams) start eight basal centrifugal spines. (This species is similar to Distephanus speculum, but has eight beams instead of six. In single pieces the number of the beams and meshes varies between seven and nine, the constant number being eight.) A seven-rayed variety is Dictyocha septenaria (loc. cit.), a nine-rayed Dictyocha polyactis.

Dimensions.—Diameter of the basal ring 0.02 to 0.03, of the apical ring 0.01 to 0.015.

Habitat.—Fossil in Tertiary rocks (Tripel and Marne from Caltanisetta, Sicily; Oran, Africa); living in the depths of the Atlantic, Station 348, and Pacific, Station 270, &c.