REPORT ON THE RADIOLARIA. 477 



Dimensions. Diameter of the phacoid shell Oil, of the medullary shell 0'04 ; length of the 

 arms 01, basal breadth 0'05, distal breadth 0'09. 



Habitat. Cosmopolitan ; Atlantic, Indian, Pacific, at various depths ; fossil in the Tertiary 

 rocks of Barbados and Nicobar. 



4. Astractura democriti, n. sp. 



Astromma aristotelis, var., Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, 



Taf. xxx. fig. 3. 

 1 Astromma aristotelis, var., Bury, 1862, Polycystins of Barbados, pi. xiv. fig. 4. 



Phacoid shell twice as broad as the medullary shell, with five to seven pores on its radius, 

 without perfect chambered ring. Arms about twice as long as broad, longer than the diameter of 

 the central disk, at the truncated distal end a little broader than at the base, and armed with 

 a strong, pyramidal, terminal spine. 



Dimensions. Diameter of the phacoid shell O'l, of the medullary shell 0'05 ; length of the 

 arms 015, basal breadth 0'04, distal breadth 0'08. 



ffalritat. Pacific, central area, Station 266, depth 2750 fathoms; fossil in Barbados. 



5. Astractura hippocratis, n. sp. 



Phacoid shell three times as broad as the medullary shell, with seven pores on its radius, 

 surrounded by two to three perfect chambered rings. Arms nearly square, scarcely as long and 

 nearly as broad as the diameter of the central disk, at the rounded distal end armed with a very 

 strong, pyramidal, terminal spine, longer than the arm itself, and at the base as broad as the 

 medullary shell. 



Dimensions. Diameter of the phacoid shell 0'09, of the medullary shell 0'03 ; length of the 

 arms 0'08, breadth O'l. 



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



Genus 209. Stauractura, 1 Haeckel, 1881, Prodromus, p. 459. 



Definition. C occodiscida with four chambered arms on the margin of the 

 circular or quadrangular disk, crossed in two equatorial diameters, connected by a spongy 

 patagium. 



The genus Stauractura differs from the foregoing in the patagium between the 

 arms, and bears therefore the same relation to it as Histiastrum in the Porodiscida does 

 to Stauralastrum. All known species of this genus form a regular square, if we connect 

 the end points of the arm axes by lines. 



Subgenus 1. Stauracturium, Haeckel. 

 Definition. Distal end of the arms blunt or truncated, without terminal spines. 



1 Stauractura Cruciform shell with four rays ; arai/fo;, XX.TIS, 



