Gate rhombic. Ring rhombic, with three prominent edges, and eight short conical curved spines arising from the lateral edges at the four corners of the rhombus. The basal and ventral spine are larger than the apical and dorsal spine; the ventral rod is more curved (with smaller angle) than the shorter dorsal rod. The medial edge of the ring is smooth, without spines. _Dimensions._--Diameter of the gate 0.08; length of spines 0.02 to 0.04. _Habitat._--South Atlantic, Station 335, depth 1425 fathoms. 5. _Zygocircus pentagonus_, n. sp. (Pl. 81, fig. 8). Gate roundish pentagonal. Ring very thick (about as thick as the radius of the gate), irregularly pentagonal, with prominent sagittal edge. On both sides of the latter arise at the five corners five pairs of short simple irregularly curved spines. The four ventral spines are larger than the four dorsal, and the two basal spines larger than the eight former, forked. (In fig. 8 the basal spines are turned upwards.) _Dimensions._--Diameter of the gate 0.07; length of the spines 0.04 to 0.06. _Habitat._--Central Pacific, Station 268, depth 2900 fathoms. {947}6. _Zygocircus hexagonus_, n. sp. Gate irregularly hexagonal. Ring obliquely hexagonal, thick, without edges, with six short and stout conical spines on the six corners. The two spines of the curved ventral rod are longer than the two spines of the straight dorsal rod. The apical spine is smaller and the basal spine larger than the four others. _Dimensions_.--Diameter of the gate 0.07 to 0.09; length of the spines 0.01 to 0.03. _Habitat_.--North Pacific, Station 241, depth 2300 fathoms. 7. _Zygocircus triquetrus_, n. sp. (Pl. 81, fig. 3). Gate obliquely ovate. Ring obliquely hexagonal, with three sharp edges and three short conical spines on each of the six corners. Therefore each hexagonal edge bears six short radial spines of equal size. _Dimensions_.--Diameter of the gate 0.04 to 0.08; length of the spines 0.01 to 0.02. _Habitat_.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface. 8. _Zygocircus dodecanthus_, n. sp. Gate semicircular. Ring semicircular or irregularly hexagonal, without edges, with twelve short blunt spines, arising in pairs from the six corners; two apical, two basal, and between them two equatorial corners. Three pairs of spines remain on the straight dorsal rod, three on the curved ventral rod. _Dimensions_.--Diameter of the gate 0.04 to 0.06; length of the spines 0.01 to 0.02. _Habitat_.--Central Pacific, Stations 263 to 268; depth 2650 to 2900 fathoms. 9. _Zygocircus acacia_, n. sp. (Pl. 81, fig. 5).