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. {959}2. _Semantrum tetrastoma_, n. sp. (Pl. 92, fig. 3). Sagittal ring semicircular, thorny, without edges. Basal ring tetragonal or nearly cordate, with a small anterior and a large posterior bow-shaped incision; on the lateral edges with numerous irregular thorns. Jugular gates pear-shaped. Cardinal gates nearly kidney-shaped. _Dimensions._--Height of the sagittal ring 0.1 to 0.14, breadth 0.07 to 0.09. _Habitat._--Central Pacific, Stations 265 to 268, depth 2700 to 2900 fathoms. 3. _Semantrum tetrapylum_, n. sp. Sagittal ring elliptical, tuberculate. Basal ring trapezoidal, also with roundish thick rods and small irregular tubercles on the margin. Jugular gates ovate, two-thirds as broad as the triangular cardinal gates. _Dimensions._--Height of the sagittal ring 0.08, breadth 0.05. _Habitat._--North Pacific, Station 253, depth 3125 fathoms. 4. _Semantrum mülleri_, Haeckel. _Stephanolithis mülleri_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi pp. 499, 539, Taf. xxxii. figs. 8_a_, 8_b_, 8_c_. Sagittal ring nearly semicircular or obliquely ovate, thorny. Basal ring also nearly semicircular, with two slight sagittal incisions (one anterior and one posterior), on the lateral edges with numerous small thorns. Jugular pores (pair I of Bütschli) pear-shaped. Cardinal pores (pair II of Bütschli) triangular. Sometimes (but not constantly) a pair of cervical bows connects the scapular bars with the subvertical dorsal rod of the sagittal ring. _Dimensions._--Height of the sagittal ring 0.09, breadth 0.06. _Habitat._--Fossil in Barbados. 5. _Semantrum sphragisma_, n. sp. Sagittal ring circular, smooth. Basal ring also nearly circular and smooth; its four basal gates of nearly equal size, elliptical or subcircular; the jugular pores scarcely smaller than the cardinal pores. All rods smooth, cylindrical, without edges and thorns. _Dimensions._--Height of the sagittal ring 0.08, breadth 0.07. _Habitat._--Tropical Atlantic, Station 347, depth 2250 fathoms; also fossil in Barbados. 6. _Semantrum bütschlii_, n. sp. Sagittal ring triangular, with vertical straight ascending dorsal rod, horizontal straight basilar rod and obliquely ascending, slightly curved ventral rod; all rods nearly cylindrical, with irregular {960}branched thorns and distorted edges. Jugular pores triangular, scarcely half as broad as the large semicircular cardinal pores. _Dimensions._--Height of the sagittal ring 0.11, breadth 0.08. _Habitat._--Fossil in Barbados. 7. _Semantrum signarium_, n. sp. (Pl. 92, fig. 4).