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 corona of spines. 



2. Phacostaurus quadrigatus, n. sp. 



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

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

 with a broad solid equatorial girdle, from which arise four crossed spines, conical, as long as the 

 radius of the disk. 



Dimensions. Diameter of the disk O2, of the outer medullary shell O'Oo, of the inner (V02 ; 

 length of the spines O'l, basal breadth 0'03. 



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



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



Astrostaurus magnificus, Haeckel, 1881, Prodromus et Atlas (pL xxxi. figs. 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. Margin 

 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 (lie 

 radius of the medullary shell. 



Dimensions. Diameter of the disk 0'22, of the outer medullary shell 0'07, of the inner i)'02f> ; 

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



Habitat. Indian Ocean, Madagascar, Eabbe, surface. 



Genus 190. Distriactis, 1 n. gen. 



Definition. Phacodiscida with simple medullary shell and with six r;idi;il 

 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. Their distance is commonly equal, rarely unequal. Either all six 

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

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

 velopment of three secondary between three primary spines. 



1. 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, silicate, half as 

 long as the radius. (Similar to Hdiosestrum medusinum, PI. 34, fig. 6.) 



w Shell with twice three rays ; 



