REPORT ON THE RADIOLARIA. 427 



Genus 184. Perizona,^ Haeckel, 1881, Prodromus, p. 457. 



Definition. — P hacodiscida with double medullary shell, without radial spines, 

 but with a solid equatorial girdle around the margin of the lenticular disk. 



The genus Perizona differs from its ancestral form Phacodiscus in the develop- 

 ment of a thin solid siliceous gii'dle, lying in the equatorial plane around the margin 

 of the disk. The two genera bear the same relation to each other that PeriphcBna 

 bears to Sethodiscus. But in the two latter genera the spherical medullary shell is 

 simple, in the two former double. 



1. Perizona scutella, n. sp. (PI. 32, figs. 7). 



Disk with smooth surface, in the distal third radiated, four times as broad as the outer, and ten 

 times as broad as the inner medullary shell. Pores subregular, circular ; thirteen to fourteen on 

 the radius of the disk, in the marginal part separated by eighty to ninety prominent radial crests, 

 which are prolonged into the proximal half of the solid girdle. Breadth of the girdle equal to that 

 of the inner meduUary shell. 



Dimensions. — Diameter of the disk 0'25, of the outer medullary shell 0'06, of the inner 0"025 ; 

 pores 0-007. 



Habitat. — Pacific, central area. Station 268, depth 2900 fathoms. 



2. Perizona pterygota, n. s-p. (PI. 32, figs. 8, 8a). 



Disk with smooth surface, six times as broad as the outer, and fifteen times as broad as the inner 

 medullary shell. Pores regularly circular ; eighteen to twenty on the radius of the disk. Margin 

 much thickened and truncated, abruptly separated in the equatorial circumference from the 

 peripheral sharp margin of the solid ghdle ; breadth of the girdle equal to that of the outer 

 medullary shell. 



Dimensions. — Diameter of the disk 0'25, of the outer medullary shell 0"04, of the inner 0'015 ; 

 pores 0'006. 



Habitat. — Pacific, central area. Station 266, depth 2750 fathoms. 



Subfamily 2. Heliosestrida, Haeckel. 



Definition. — P hacodiscida with a constant number of radial spines on the 

 margin of the disk (two, three, four, six, or eight), which are commonly regularly 

 disposed (sometimes more or less irregularly). 



* Perii!!orea= Shell with surrounding girdle ; ts^/, i^omvi. 



