REPORT ON THE RADIOLARIA. 435 



prismatic, with prominent edges, about as long as the diameter of the disk, and as broad as the 

 girdle. 



Dimensions. — Diameter of the disk OiG, of the medullary shell 0'08 ; length of the crossed 

 spines 0-18, breadth 002. 



Habitat. — Pacific, central area, Station 268, depth 2900 fathoms. 



7. Sethostaurus gigas, n. sp. 



Disk with smooth surface, four times as broad as the medullary shell. Pores regular, circular ; 

 twenty to twenty-two on the radius. Margin of the disk with a narrow solid girdle, bearing on 

 the periphery one hundred to one hundred and twenty slender flat pointed teeth. Four crossed 

 spines equal, conical, about as long as the radius of the disk, as Ijroad at their furrowed base as the 

 radius of the medullary shell. 



Dimensions. — Diameter of the disk 0'4, of the medullary shell 01 ; length of the crossed spines 

 0'5, basal breadth 0'05. 



Habitat. — Western Tropical Pacific, Station 225, depth 4475 fathoms. 



Genus 189. Phacostaurus,^ Haeckel, 1881, Prodromus, p. 457. 



Definition. — P h a c o d i s c i d a with double medullary shell and with four radial 

 spines on the margin of the disk, crossed in the equatorial plane. 



The genus Phacostaurus differs from the foregoing Sethostaurus by the duplication 

 of the medullary shell, and beais to it the same relation as Phacodlscvs does to 

 Scthodiscus. Also in this genus the cross of the shell is commonly regular, rectangular, 

 sometimes more or less irregular. 



Subgenus 1. Phacostaurium, Haeckel. 



Definition. — Margin of the disk without a solid equatorial girdle or a corona of 

 spines. 



1. Phacostaurus oceanidum, n. sp. (PI. 31, fig. 6). 



Disk with smooth surface, three times as broad as the outer and eight times as broad as the inner 

 medullary shell. Pores regular, circular ; eleven to twelve on the diameter of the disk. Margin 

 smooth. Four crossed spines pyramidal, deeply sulcate, about as long as the diameter of the outer 

 medullary shell, and two-thirds as broad at the base. 



Dimensions. — Diameter of the disk Olo, of the outer medullary shell O'Oo, of the inner 0'02 ; 

 length of the spines 0'05, basal breadth- 0-0.3. 



Habitat. — Central Pacific, Station 266, depth 2750 fathoms. 



' Phacostavrvs - Lens •with cross ; (paxi;, urav^nc. 



