430 THE VOYAGE OF H.M.S. CHALLEls'GETl. 



6. Sethostylus spicatus, n. sp. 



Disk with spiny surface, four times as broad as the medullary shell. Pores irregular roundish, 

 with many unequal conical spines between them. Margin with an equatorial girdle, composed of 

 three to four concentric series of conical radial spines, about as long as the radius of the medullary 

 shell. Both main spines very large, cylindrical, longer than the diameter of the disk, and as 'broad 

 as the radius of the medullary shell. 



Dimensions. Diameter of the disk O2, of the medullary shell 0'05 ; length of the main spines 

 0-3 or more, breadth 0'025. 



Habitat. Fossil in the rocks of Barbados, Haeckel; living in the depths of the Equatorial Atlantic, 

 Station 348, depth (2450) fathoms. 



Genus 186. Phacostylus, 1 Haeckel, 1881, Prodromus, p. 457. 



Definition. P hacodiscida with double medullary shell and with two radial 

 spines on the margin of the disk, opposite in the equatorial axis. 



The genus Phacostylus differs from the foregoing Sethostylus by the duplication 

 of the medullary shell, and bears the same relation to it as Phacodiscus does to Setho- 

 discus, or as Amphicydia in the Coccodiscida does to Stylocyclia. 



Subgenus 1. Phacostylium, Haeckel. 



Definition. Margin of the disk simple, smooth, without equatorial girdle, and 

 without a corona of marginal spines. 



1. Phacostylus amphistylus, n. sp. (PI. 31, fig. 12). 



Disk with smooth surface, four times as broad as the outer, and twelve times as broad as the 

 inner medullary shell. Pores regular, circular ; twelve to fourteen on the radius of the disk. Margin 

 of the disk simple, smooth, without spines and equatorial girdle. Both polar spines conical, longer 

 than the diameter of the disk, furrowed at the base, and twice as broad as the inner medullary 

 shell. 



Dimensions. Diameter of the disk 016 to 018, of the outer medullary shell 0'045, of the 

 inner 0'015 ; length of the polar spines 0'2, basal breadth 0'03. 



Habitat. Pacific, central area, Station 272, depth 2600 fathoms. 



2. Phacostylus amphixiphus, n. sp. 



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

 inner medullary shell. Pores irregular, roundish ; ten to eleven on the radius. Margin of the disk 



1 Phacostylui='Leos with styles ; tpnos, 



