436 THE VOYAGE OF H.M.S. CHALLENGER. 



Subgenus 2. Astrostaurus, Haeckel, 1881, Prodromus, p. 457. 

 Definition. — Margin of the disk with a solid equatorial girdle, or a <;orona of spines. 



2. Phacostaurus quadrigatvs, n. sp. 



Disk with smooth surface, four times as broad as the outer and ten times as broad as the inner 

 medullary sliell. Pores irregular, roundish ; fifteen to sixteen on the diameter of the disk. Margin 

 with a broad sohd equatorial girdle, from which arise four crossed spines, conical, as long as tlie 

 radius of the disk. 



Dimensions. — Diameter of the disk 0-2, of the outer medullary shell 0-05, of the inner 0'02 ; 

 length of the spines O'l, basal breadth O'OS. 



Habitat. — South Pacific, Station 300, depth 1375 fathoms. 



3. Phacostaurus magnificus, n. sp. (PI. 31, figs. 7, 8). 



Astrostaurus riuujnificus, Haeckel, 1881, Prodromus et Atlas (pi. xxxi. fiys. 7, 8). 



Disk with smooth surface, three times as broad as the outer and nine times as broad as the inner 

 medullary shell. Pores regular, circular ; thirteen to fourteen on the diameter of the disk. Mai'gin 

 with a corona of fifty to sixty conical spines of unequal length. Four spines of the cross very large 

 pyramidal, deeply sulcated, longer than the radius of the disk, and as broad at the base as the 

 radius of the medullary shell. 



Dimensions. — Diameter of the disk 0-22, of the outer medullary shell 0-07, of the inner 0-02.'i ; 

 length of the four spines 0'16, basal breadth 0'04. 



Habitat. — Indian Ocean, Madagascar, Eabbe, surface. 



Genus 190. Distriactis,^ n. gen. 



Definition. — Pbacodiscida with simple medullary shell and with six radial 

 spines on the margin of the disk placed in the equatorial plane. 



The genus Distriactis exhibits on the margin of the lenticular phacoid shell six 

 radial solid spines. Then- distance is commonly equal, rarely unequal. Either all six 

 spines are of equal size and similar form, or three larger (perradial) alternating wdth three 

 smaller (interradial), so that Distriactis appears to be derived from Triactiscus by de- 

 velopment of three secondary between three primary spines. 



I. Distriactis liriantha, n. sp. 



Disk smooth, four times as broad as the medullary shell, with regular, circular pores (about ten 

 on the radius). Six marginal spines of equal size and at equal distances, triangular, sulcate, half as 

 long as the radius. (Similar to Helioscstntm med^isinum, PL 34, fig. 6.) 



1 i35s;Wndi's = Shell with twice three rays ; oiaTpiaini;. 



