REPORT ON THE RADIOLARIA. 817 



Radial spines strongly compressed, two-edged ; outer half shorter than the inner. By-spines 

 undulate, half as long as the radius. 



Dimensions. Diameter of the shell 012, of the parmal pores 0'02 to O03, of the sutural pores 

 0-003 to 0-004 



Habitat. South Pacific, Station 287, surface. 



Subgenus 2. Diporaspidium, Haeckel. 



Definition. Shell with fifty-four sutures, four polar plates on each pole of the 

 main axis different in pairs : two major hexagonal meeting in a polar (" geotomical ") 

 suture, two minor pentagonal, not meeting together (separated by that suture). Shell 

 therefore composed of eight hexagonal plates (four equatorial and four polar) and of 

 twelve hexagonal plates (eight tropical and four polar). 



3. Diporaspis zygopora, n. sp. 



Shell with fifty-four sutures and fifty-four circular sutural pores : with eight hexagonal and 

 twelve pentagonal plates. Both aspinal pores of each plate elliptical, three times as broad as the 

 sutural pores. Radial spines compressed, two-edged ; outer half shorter than the inner. By-spines 

 very numerous, simple, one-third as long as the radius, forming coronels or elegant circles around the 

 pores (a small coronel around each sutural pore, a large one around each couple of aspinal pores). 



This typical species is nearly allied to Dorataspis typica (PI. 138, fig. 4), and may be derived 

 from it by development of the coronels of by-spines. 



Dimensions. Diameter of the shell 0'16, aspinal pores 0'03, sutural pores O'Ol. 



Habitat. Central Pacific, Station 271, surface. 



Genus 353. Oropliaspis, 1 Haeckel, 1881, Prodromus, p. 468. 



Definition. D orataspida with twenty plates, which are perforated by forty 

 aspinal pores (two pores in each plate). Surface of the shell without combs, dimples, 

 and by-spines. Each radial spine bears outside of the shell two opposite free apophyses, 

 which are either simple or branched. 



The genus Oropliaspis differs not only from its ancestral form, Dorataspis, but 

 from all other Dorataspida in the development of peculiar free apophyses on the radial 

 spines, outside the shell. These apophyses, two being opposite on each spine, appear 

 as a repetition of the primary apophyses of Phractaspis ; they are either simple or 

 branched, and sometimes the branches are united together, forming an outer free shield 

 with two or four pores. These outer plates represent the beginning of a second outer 

 shell and form the transition to Phractopelta, the ancestral form of the Phractopeltida. 



1 Orophaspis = Roof shield ; ojopof, dim's. 

 (ZOOL. CHALL. EXP. PART XL. 1885.) Rr 103 



