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



3. Hexacromyum arachnoides, n. sp. 



Hexacrornidium arachnoides, Haeckel, 1881, Prodromus, p. 453. 



Shell composed of four concentric shells, with radial proportion = 1:2:3:4. Innermost shell 

 with regular, hexagonal meshes ; the three other shells with irregular, polygonal meshes ; bars 

 between the large meshes in all four shells very thin, cobweb-like. Surface covered with thin 

 bristle-shaped by-spines, as long as the radius. Six radial main spines three-sided prismatic, 

 longer than the diameter of the whole shell. 



Dimensions. Diameter of the four shells (A) 008, (B) 016, (C) 0'24, (D) 0'32 ; length of the 

 spines 0'4, breadth O'Ol. 



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



4. Hexacromyum octahedrum, n. sp. (PL 23, fig. 2). 



Shell composed of four concentric shells which are not spherical (as in the three preceding 

 species), but regular octahedral. Radial proportion =1 : 2 - 5 : 6 : 9. Network in all four shells 

 delicate, with irregular polygonal meshes and thin bars ; the thickness of the bars and size of the 

 meshes increasing from the innermost to the outermost shell. Six radial spines three-sided 

 prismatic, increasing slowly in breadth towards the distal end, much longer than the shell 

 diameter. 



Dimensions. Diameter of the four shells (A) 0'02, (B) 0'05, (C) 012, (D) 0'18 ; length of the 

 radial spines 0'2 to 0'3 and more, breadth O'Ol. 



Habitat. Central Pacific, Station 263, depth 2650 fathoms. 



Subfamily HEXACARYIDA, J Haeckel, 1881, Prodromus, p. 454. 

 Definition. C ubosphserida with five or more concentric lattice-shells. 



Genus 83. Cubosphcera, 2 n. gen. 



Definition. C ubosphaerida with five to six or more concentric lattice-shells 

 and six simple spines of equal size. 



The genus Cubosphara is developed from the preceding Hexacromyum by further 

 addition of the concentric lattice-shells, their number amounting to five, six, or more. 

 The innermost two of 'these are medullary shells, the others being cortical shells. All are 

 connected by six radial beams, prolonged outside into six simple spines of equal size ; 

 these lie opposite in pairs in three dimensive axes, corresponding to the three axes 

 of a cube. 



1 Hexacaryida = Cubospharida multiplicia = Polysphserida hexacantha. 



2 Cubosp]uera = Sphere with the three axes of a culms ; x,v/3os, <r^i. 



