Gate obliquely ovate. Ring semi-ovate, with straight dorsal and curved ventral rod, partly with distorted edges. Six bunches of numerous short and straight conical spines arise from the ring, one larger bunch (often trifid) from the apex, two smaller bunches from the dorsal, two from the ventral rod, and one very large bunch from the base. The six bunches are often more separated, smaller, and the spines shorter than in the figured specimen, which passes over into _Dendrocircus_. _Dimensions_.--Diameter of the gate 0.12 to 0.16; length of the spines, 0.01 to 0.07. _Habitat_.--Central Pacific, Station 266, depth 2750 fathoms. 10. _Zygocircus polygonus_, n. sp. (Pl. 81, fig. 2). Gate irregularly roundish or ovate. Ring irregularly polygonal or sometimes nearly circular, without edges, armed with a single series of ten to fifteen short pyramidal spines, which are irregularly {948}disposed in the sagittal plane. The ventral rod is strongly curved, often semicircular, the dorsal rod less curved or nearly straight. _Dimensions_.--Diameter of the gate 0.05 to 0.07; length of the spines 0.004 to 0.02. _Habitat_.--Cosmopolitan--Atlantic, Pacific; also fossil in Barbados. 11. _Zygocircus bütschlii_, n. sp. _Zygocircus productus_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi. p. 497. Gate obliquely ovate. Ring irregularly roundish, semi-ovate or ovate, with interrupted and distorted edges, and with a large number (ten to twenty or more) of simple, irregularly formed and asymmetrically disposed spines; commonly some larger spines at the base. _Dimensions_.--Diameter of the gate 0.05 to 0.09; length of the spines 0.005 to 0.02. _Habitat_.--Fossil in Barbados. 12. _Zygocircus productus_, Bütschli. _Zygocircus productus_, Bütschli, 1882, Zeitschr. f. wiss. Zool., vol. xxxvi p. 496. _Lithocircus productus_, R. Hertwig, 1879, Organismus d. Radiol., p. 69, Taf. vii. fig. 4. Gate obliquely ovate. Ring obliquely ovate, with three complete prominent edges and with numerous (ten to twenty or more) simple, short conical spines, arising in three series from the three edges; commonly some smaller spines at the base. _Dimensions_.--Diameter of the gate 0.1 to 0.2; length of the spines 0.005 to 0.02. _Habitat_.--Cosmopolitan; Mediterranean, Atlantic, Pacific, surface. Genus 404. _Dendrocircus_,[23] Haeckel, 1881, Prodromus, p. 447. _Definition_.--#Stephanida# with a simple dipleuric or bilateral ring, armed with branched spines, without typical basal feet. The genus _Dendrocircus_ has the same dipleuric or bilaterally symmetrical form of the sagittal ring as its ancestral genus _Zygocircus_. It differs from the latter in the development of branched radial spines, and therefore bears to it the same relation as the amphithect _Lithocircus_ does to the simpler _Archicircus_. 1. _Dendrocircus quadrangulus_, n. sp.