Page:Scientific results HMS Challenger vol 18 part 2.djvu/85

Rh sagittal pair, one posterior and one anterior). All six gates of the basal plate triangular, the jugular and cervical a little smaller than the cardinal gates.

Dimensions.—Height of the sagittal ring 0.1, breadth 0.07.

Habitat.—Tropical Atlantic, Station 348, depth 2450 fathoms.

3. Semantidium haeckelii, Bütschli.

Stephanolithis Haeckelii, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. pp. 499, 538, Taf. xxxii. figs. 6a, 6b.

Sagittal ring elliptical, with three pairs of short horizontal branched spines, one apical and two equatorial pairs (one dorsal and one ventral). Basal ring roundish hexagonal, with numerous short thorns on the margin. Jugular pores ovate, about half as broad as the ovate cardinal pores and twice as broad as the small cervical pores.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.06.

Habitat.—Fossil in Barbados.

4. Semantidium signatorium, n. sp. (Pl. 92, fig. 7).

Sagittal ring semicircular, thorny; basal ring pentagonal, with short spines on the margin and five stronger thorny spines on the five corners. Jugular pores ovate, smaller than the triangular cervical pores. Cardinal pores two to three times as large as each of the former, pentagonal.

Dimensions.—Height of the sagittal ring 0.08, breadth 0.12.

Habitat.—North Pacific, Station 341, depth 2300 fathoms.

Definition.— with a variable number of pores on the apical and the basal part of the ring, symmetrically arranged, without typical basal feet.

The genus Clathrocircus comprises those Semantida in which the sagittal ring bears not only basal pores (as in the three preceding genera) but also apical pores (on the opposite pole of the main axis), or a variable number of pores along the whole ring. All these pores are symmetrically arranged in pairs. In the simplest form there are only two apical pores opposite to four basal pores, whilst in the highest state of development the whole ring bears two complete circles of pores. At both poles of the transverse axis two large lateral gates remain open. If these become closed by lattice-work, Clathrocircus passes over into Dictyospyris.