334 THE VOYAGE OF H.M.S. CHALLENGEK. 



Subgenus 4. XiphatraQtium, Haeckel. 



Definition. — Network of the cortical shell irregular, with meshes of unequal size 

 or dissimilar form ; surface thorny or papillose. 



7. Xiphat7'actus radiosus, Haeckel. 



StylospluEra radiosa, Ehrenberg, 1875, Abhandl. d. k. Akail. il. Wiss. Berlin, p. 84, Taf. xxiv. 

 fig. 5. 



Cortical shell very thick walled, with thorny surface, and irregular, roundish j)ores, once to three 

 times as broad as the bars ; nine and ten on the half equator. Polar spines conical, on the base 

 about as broad as the largest pores ; the larger as long as the main axis, the smaller scarcely one- 

 fourth as long. (The radial striation, figured Ijy Ehrenberg and applied to the name of this species, 

 is produced by the contours of the fuunel-sliaped pores in the thick walls seen in optical section ; 

 the ellipsoidal cortical shell is double.) 



Dimensions. — Major axis 013, minor 0"09 ; pores O^OO-S to O'Ol, bars 0'003 ; main axes of the 

 two medullary shells 0"05 and 0'03 ; length of the major polar spine 0'12, of the minor 0-03, 

 basal breadth O'Ol. 



Habitat. — Fossil in the Tei'tiaiy rocks of Barbados. 



8. Xiphatractus glyptodon, u. ,sp. (PI. 17, figs. 9, 10). 



Cortical shell thick walled, covered with radial spines of the size of the pores; on the half 

 equator eight to ten irregular or subregular roundish pores, twice to four times as broad as the bars. 

 In the bottom of each pore a thin lamella of silex, perforated by four to six smaller roundish pores. 

 Both medullary shells (fig. 10) spherical, with smaller, regular, circular pores. Larger polar spine 

 three-sided pyramidal, in lengtli equals the main axis ; sliorter spine only half as long, but twice as 

 thick, of elegant pommel-form (fig. 9), with nine prominent edges. 



Dimensions. — Major axis 0'12, minor 01 ; pores and spines O'Ol to 0'02, bars and porules 0'005 ; 

 diameter of the two medullary sheUs 0'05 and 0'02 ; length of the major polar spine 01, of the 

 minor 0'06, greatest thickness 0'04. 



Habitat. — Pacific, central area, Station 2fi3, surface. 



Genus 141. Cromyatractus,^ n. gen. 



Dejinition. — Druppulida witli four or more concentric shells (two medullary 

 shells and two or more cortical shells), in the main axis with two large opposite polar 

 spines of equal size and similar form. 



The genus Cromyatractus is very nearly allied to all the foregoing genera, which 

 bear two equal spines opposite to one another on the poles of the main axis ; it differs 



' Cro wiyatrac/ MS — Onion-spindle ; y.^ofivou, a.T^ax.To;. 



