REPOKT ON THE RADIOLARIA. 263 



inner cortical shell also with irregular, polygonal pores, three to nine times as broad as the thick 

 bars. Both medullary shells with subregular, circular pores (the outer three times as broad as the 

 inner). Eaclial spines twelve to twenty, three-sided prismatic, stout, piercing the three outer 

 shells, inserted on the innermost ; their outer part pyramidal, half as long as the radius. 



Dimensions. Diameter of the four shells (A) 0"22, (B) 015, (C) 0'07, (D) 0'03; meshes of 

 the outer shell 0'02 to 0'04; length of the outer spines 0'05. 



Habitat. Central Pacific, Station 266, depth 2750 fathoms. 



8. Cromyomma mucr onatum, n. sp. (PL 30, figs. 5, 5a). 



IJadial proportion of the three spheres = 1:2:3:6. Outer cortical shell thin walled, with 

 large, irregular, roundish pores and crested three-sided bars; inner cortical shell with regular, 

 circular, hexagonally formed pores (four times as broad as the bars). Both medullary shells with 

 simple, small, regular, circular pores (fig. 5a). Twelve radial spines three-sided prismatic, dagger- 

 shaped, with three teeth, as long as the diameter of the innermost shell. 



Dimensions. Diameter of the four shells (A) 0'24, (B) 012, (C) 0'08, (D) 0'04 ; meshes of 

 the outer shell 0'02 to 0'04; length of the spines 0'04. 



HalUat. Central Pacific, Station 274, depth 2750 fathoms. 



Genus 105. Or omy echinus, 1 Haeckel, 1881, Prodromus, p. 454. 



Definition. A strosphasrida with four concentric lattice-spheres and numerous 

 simple spines of two different kinds ; larger main spines and smaller by-spines. 



The genus Cromyechinus differs from Cromyomma in the same way as Echinomma 

 from Actinomma ; the radial spines being differentiated into two different kinds ; a larger 

 number of small by-spines, and a smaller number of large main spines. 



1. Cromyechinus icosacanthus, n. sp. (PI. 30, fig. 1). 



I 



Eadial proportion of the three spheres = 1 : 2 :' 6 : 8. Outer cortical shell very delicate, with 

 very small, regular, circular pores, covered with very numerous bristle-shaped by-spines, half as long 

 as the radius ; inner cortical shell with very large, irregular, polygonal pores, three to eight times 

 as broad as the bars. Both medullary shells with regular, circular pores, connected with the 

 former by twenty regularly disposed, very thin bars ; these are prolonged outside into twenty very 

 stout, three-sided prismatic main spines, as long as the radius, which arise from the inner cortical 

 shell, and at the distal end are cuspidate. 



Dimensions. Diameter of the four shells (A) 016, (B) 013, (C) 0'04, (D) 0'02 ; pores of the 

 outer cortical shell O'OOS, of the inner 0'03, bars 0'003 ; length of the spines O'OS. 



Habitat. Central Pacific, Station 271, depth 2425 fathoms. 



1 Cromyechinus = Onion-shaped Urchin; K^OXVOH, i%in<is. 



