Gate ovate or nearly elliptical. Ring ovate, with three prominent edges, and numerous richly branched spines arising from the three edges. The specimen figured, which I observed living in the Mediterranean, exhibited eight bunches of larger spines, three dorsal, three ventral, one apical, and one basal bunch; the latter much larger than the seven others. Each bunch was composed of two to four larger and numerous smaller spines, their branches curved and forked. The ovate purple central capsule, with a distinct podoconus, filled more than the half of the gate. _Dimensions_.--Diameter of the gate 0.1 to 0.13; length of the spines 0.05 to 0.15. _Habitat_.--Mediterranean (Portofino, 1880), Atlantic (Canary Islands), Station 354, surface. Genus 403. _Zygocircus_,[22] Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 496. _Definition_.--#Stephanida# with a simple dipleuric or bilateral ring, smooth or thorny, without branched spines and basal feet. The genus _Zygocircus_ and the following _Dendrocircus_ differ from the two preceding older genera in the bilaterally symmetrical or dipleuric form of the sagittal ring. Whilst in _Archicircus_ and _Lithocircus_ the two sagittal halves or bows of the ring, the dorsal and ventral bow, are equal (therefore the fundamental form amphithect or diphragmatic), here both bows become distinctly different; the dorsal bow is constantly more straight (often vertical), the ventral bow more convex (obliquely ascending). This dipleuric differentiation is most important, as it is transmitted to the greater number of NASSELLARIA by heredity. {946}1. _Zygocircus sagittalis_, n. sp. Gate ovate. Ring half ovate or nearly triangular, with three curved edges and three prominent corners, one apical and two basal protuberances. Dorsal rod vertical, twice as long as the horizontal basal rod. Ventral rod convexly curved. _Dimensions._--Diameter of the gate 0.05 to 0.07; height of the tubercles 0.01 to 0.015. _Habitat._--Central Pacific, Stations 265 to 268, depth 2900 fathoms. 2. _Zygocircus trigonus_, n. sp. Gate triangular. Ring triangular, with three curved edges and three prominent corners, which are prolonged into nine divergent conical spines; three spines arising from the three edges of each corner. Dorsal rod vertical; ventral and basal rods curved and convergent. _Dimensions._--Diameter of the gate 0.11 to 0.13; length of the spines 0.01 to 0.015. _Habitat._--Indian Ocean, Sunda Archipelago (Rabbe), surface. 3. _Zygocircus tetragonus_, n. sp. Gate ovate. Ring quadrangular, without edges, with four simple conical spines of different sizes; one smaller apical, one larger basal, and two equatorial spines of middle size (one dorsal and one ventral). Dorsal and ventral rod curved. _Dimensions._--Diameter of the gate 0.04 to 0.06; length of the spines 0.018 to 0.026. _Habitat._--Tropical Atlantic, Station 338, depth 1990 fathoms. 4. _Zygocircus rhombicus_, n. sp.