946 THE VOYAGE OF H.M.S. CHALLENGER. 



1. Zygocircus sagittalis, n. sp. 



Gate ovate. Eing 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. Zygocirmis trigonus, n. sp. 



Gate triangular. Eing 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 Oil to 013 ; length of the spines O'Ol to 0'015. 



Habitat. — Indian Ocean, Sunda Archipelago (Eabbe), surface. 



3. Zygocircus tetragonus, n. sp. 



Gate ovate. Eing 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 O'Ol to 0'06 ; length of the spines O'OIS to 0'026. 



Habitat. — Tropical Atlantic, Station 338, depth 1990 fathoms. 



4. Zygocircus rhomhicus, n. sp. 



Gate rhombic. Eing 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 pentagomis, n. sp. (PI. 81, fig. 8). 



Gate roundish pentagonal. Eing 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. 



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