REPORT ON THE RADIOLARIA. 479 



rows of chambers ; it connects the end points of the arm radius in such a manner that the whole 

 shell becomes a regular square. 



Dimensions. Diameter of the phacoid shell 0'09, of the medullary shell 0'045 ; length of the 

 arms 01, greatest breadth O08. 



Habitat. South Pacific, Station 295, depth 15#0 fathoms. 



Genus 210. Pentactura, 1 Haeckel, 1881, Prodromus, p. 459. 



Definition. Coccodiscida with five chambered arms on the margin of the 

 circular or pentagonal disk, without a connecting patagium. 



The genus Pentactura possesses five free radial arms, and resembles Pentalastrum 

 among the Porodiscida. The distance of the five arms seems to be sometimes equal, 

 at other times different in one and the same species. 



1. Pentactura pentactis, Haeckel. 



Antromma pentactis, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, p. 66, Taf. xxx. 



fig. 1. 



Phacoid shell two and a half times as broad as the medullary shell, with eight pores on its 

 radius. Arms regularly or irregularly disposed, nearly square, about half as large as the phacoid 

 shell, at the truncated distal end little broader than at the base. In the specimen figured, and very 

 imperfectly described by Ehreuberg, (loc. cit.), the arms were asymmetrically disposed, two opposite 

 in one axis of the disk, two others on one side of this axis, the fifth opposite to these on the other 

 side. Another specimen which I found in the Barbados rocks had five arms of equal size, regularly 

 disposed, at equal intervals. 



Dimensions. Diameter of the phacoid shell 01, of the medullary shell 0'04 ; length and breadth 

 of the arms 0'05 to 0'06. 



Habitat.- Fossil in the rocks of Barbados. 



2. Pentactura astropecten, n. sp. 



Phacoid shell three times as broad as the medullary shell, with ten pores on its radius. Arms 

 regularly disposed, club-shaped, nearly twice as long as the diameter of the phacoid shell, and equal 

 to it in breadth at the rounded distal end. The latter is armed with a short conical spine, and in 

 twice as broad as the base. 



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

 arms 017, basal breadth 0'05, distal breadth 0'08. 



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



1 Pentactura = Stellated shell with five rays ; aim, eixri'i, 



