REPORT ON THE RADIOLARIA. 589 



and forming a larger lanceolate disk of looser framework. (Similar in form to Amphymenium 

 pupula, PI. 44, fig. 8, but with an irregular spongy framework and pointed ends.) 



Dimensions Eadius of the arms 016, breadth 0'05 ; major axis of the lanceolate patagium 0'32, 

 minor axis 0'12. 



Habitat Pacific, central area, Station 270, surface. 



Genus 262. Rkopalodictyum, 1 Ehrenberg, 1860, Monatsber. d. k. preuss. Akad. 



d. Wiss. Berlin, p. 830. 



Definition. S pongodiscida with three spongy arms on the margin of the 

 circular or triangular disk, without a connecting patagium. 



The genus Rhopalodictyum comprises those, very common forms of Spongodiscida in 

 which the margin of the disk is provided with three simple, free, spongy arms. It 

 corresponds to Dictyastrum and Rhopalastrum among the Porodiscida, to Trigonactura 

 among the Coccodiscida. The typical species of this genus is Rhopalodictyum abyssorum 

 of Ehrenberg, the only species figured by him. His diagnosis of the genus was very 

 insufficient, and agreed with that of his Dictyastrum (compare above the improved 

 diagnosis of this genus, p. 526, and my Monograph, p. 466). 



Subgenus 1. Rhopalodictya, Haeckel. 

 Definition. Triangular shell regular, with three arms of equal size and equidistant. 



1. Rhopalodictyum abyssorum, Ehrenberg. 



Rhopalodidyum abyssorum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 299, 

 Taf. viii. fig. 17. 



Arms of equal size and equidistant, club-shaped, about as long as the diameter of the triangular 

 central disk, and a little longer than the breadth of the pear-shaped rounded distal end. Surface 

 rough. 



Dimensions. Eadius of the arms O'll, basal breadth 0'03, distal breadth 0'06. 



Habitat. Cosmopolitan ; Atlantic, Indian, Pacific ; tropical zone, surface. 



2. Rhopalodictyum truncatum, Ehrenberg. 



Rhopalodictyum truncatum, Ehrenberg, 1861, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, 



p. 301. 



1 Dictyastrum angulatum, Ehrenberg, 1872, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 289, 

 Taf. viii. fig. 18. 



Arms of equal size and equidistant, nearly square, with straight edges, towards the truncated end 

 a little broader, about of the same diameter as the central triangular disk. This species is indicated 



1 Rhopalodictyum = Network with clubs; poV 



