REPORT ON THE RADIOLARIA. 469 



irregular, roundish ; ten on the radius of the phacoid shell, a single one on each chamber of the 

 equatorial girdle. Margin of the disk with numerous strong conical radial spines of different 

 breadths, arranged in several circles, the strongest in the equatorial plane, about as broad as one 

 ring and twice as long. Surface thorny. v 



Dimensions. Diameter of the disk (with seven rings) 0'3, of the phacoid shell 0'12, of the outer 

 medullary shell 0'05, of the inner - 02. 



Habitat. Pacific, central area, Station 268, depth 2900 fathoms ; also fossil in Barbados. 



Subfamily 3. ASTRACTUBIDA, Haeckel, 1881, Prodromus, p. 458. 



Definition. C occodiscida with two or more (commonly three or four) 

 chambered radial arms on the margin of the disk, situated in its equatorial plane (with 

 or without a connecting patagium between the arms). 



Genus 204. Diplactura? Haeckel, 1881, Prodromus, p. 458. 



Definition. C occodiscida with two opposite chambered arms on the margin of 

 the circular disk, without a connecting patagium. 



The genus Diplactura is the simplest form of the Astracturida, or of those 

 Coccodiscida in which the margin of the disk bears chambered arms, situated in its 

 equatorial plane. This subfamily corresponds to the Euchitonida among the Porodiscida, 

 to the Spongobrachida among the Spongodiscida. In Diplactura there are only two 

 free arms, opposite in one equatorial diameter (corresponding to Amphibrachium among 

 the former, to Spongolene among the latter). 



Subgenus 1. Diplacturium, Haeckel. 

 Definition. Arms blunt at the distal end, without radial spines. 



1. Diplactura diplobrachia, n. sp. 



Phacoid shell twice as broad as the medullary shell, with six pores on its radius, without a perfect 

 chambered ring around it. Arms club-shaped, one and a half times as long as the diameter of the 

 phacoid shell, at the distal end rounded, blunt, as broad as the latter, at the base only half 

 as broad. 



Dimensions.-^-DiameteT of the phacoid shell 0'08, of the medullary shell 0'04 ; length of the 

 arms 012, basal breadth 0'04, distal breadth 0'08. 



Habitat. Pacific, central area, Station 265, depth 2900 fathoms. 



1 -Dipr<c(ura=Stellated shell with double tail ; SiVxoi/f, dxri;, ot>. 



