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



Genus 198. Stylocydia, 1 Ehrenberg, 1847, Monatsber. d. k. preuss. Akad. d. Wiaa. 



Berlin, p. 54. 



Definition. C occodiscida with two opposite solid radial spines on the margin 

 of the circular disk. Medullary shell simple. 



The genus Stylocydia opens the series of the Stylocyclida or of those Coccodiscida 

 in which the margin of the chambered disk is armed with solid radial spines, situated 

 in its equatorial plane, but without chambered arms. Stylocydia is the most simple 

 form of this subfamily, and bears only two marginal spines, opposite in one equatorial 

 axis of the disk. The medullary shell is simple. This genus corresponds to 

 Xiphodictya in the family Porodiscida. The genus was previously known only by one 

 single species described by Ehrenberg. 



1. Stylocydia dimidiata, Ehrenberg. 



Stylocydia dimidiata, Elirenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 84, Taf. xxix. 



fig. 4. 



Phacoid shell three times as broad as the medullary shell, surrounded by five to eight 

 chambered rings of equal breadth, divided by eighty to ninety piercing radial beams into square 

 chambers. Pores subregular, circular ; six to seven on the radius of the phacoid shell, a single one 

 on each chamber. Both opposite marginal spines strong, club-shaped, their thickness decreasing from 

 the margin towards the centre of the disk. (The figure of Ehrenberg is very incomplete.) 



Dimensions. Diameter of the disk (with eight rings) 0'25, of the phacoid shell (Ml, of the 

 medullary shell 0'035. 



Habitat. Fossil in the Tertiary rocks of Barbados ; living in the depths of the Equatorial 

 Atlantic, Station 348, depth (2450) fathoms. 



2. Stylocydia prionacantha, n. sp. (PI. 37, fig. 6). 



Phacoid shell two and a half times as broad as the medullary shell, surrounded by five to six 

 chambered rings, which are divided by fifty to sixty piercing radial beams into square chambers. 

 Pores in the thick -walled phacoid shell regularly circular, increasing in size from the centre ; 

 eight to nine on its radius. Pores on the surface of the chambered girdle smaller, very irregular, 

 two to three on each ring. Both marginal spines longer than the diameter of the disk, with broad 

 serrated edges. 



Dimensions. Diameter of the disk (with five rings) 0-23, of the phacoid shell 012, of tha 

 medullary - 05. 



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



1 Stylocydia = Circular shell with styles ; vrfao;, xt/xx/o. 



