Page:Scientific results HMS Challenger vol 18 part 2.djvu/82

958 6. Semantis spinescens, Haeckel.

Stephanolithis spinescens, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p.160, Taf. i. fig. 29.

Stephanolithis spinescens, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497, Taf. xxxii. figs. 7a, 7b.

Sagittal ring ovate with four pairs of thin, irregularly branched spines, two apical pairs, one on the straight dorsal rod and one on the curved ventral rod. Basilar rod with a posterior and an anterior forked rod (commencing caudal and sternal foot). Basal ring square, with two lateral spines, and two triangular gates scarcely one-third as broad as the ring-gate. An internal ascending procolumna (rod c$1$ in the figure of Bütschli) connects the basal and ventral rods of the sagittal ring.

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

Habitat.—Fossil in Barbados.

Definition.— with four basal pores (two anterior jugular and two posterior cardinal pores), without typical basal feet.

The genus Semantrum, one of the most important of the, arises from the preceding Semantis by duplication of the two basal gates. Behind the pair of coracal rods there arises from the basilar rod of the sagittal ring a third pair of lateral horizontal branches, the scapular rods. These become connected with the coracal rods on each side, and so produce a second posterior pair of basal pores, the "cardinal gates." These are constantly larger than the anterior "jugular gates." Therefore the vertical ring of Semantrum possesses a horizontal basal ring with four very characteristic gates, enclosed by three pairs of lateral curved and connected branches, and these become transmitted by heredity to the majority of the.

1. Semantrum quadrifore, n. sp. (Pl. 92, fig. 5).

Sagittal ring subcircular or ovate, with three edges and four sagittal forked spines on the odd edge (two dorsal and two ventral spines). Basal ring decagonal, with ten simple or forked spines on the ten corners. Jugular gates tetragonal. Cardinal gates pentagonal.

Dimensions.—Height of the sagittal ring 0.09, breadth 0.07.

Habitat.—Tropical Atlantic, Station 351, surface.