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



Inner aperture of each pore closed by a thin fenestrated lamella with five to seven small pores. 

 Major polar spine three-sided pyramidal, longer than the diameter of the outer sphere ; minor polar 

 spine scarcely as long as its radius, pommel-shaped. (Similar to Xiphatractus glyptodon, PI. 17, 

 figs. 9, 10, but differs in the spherical, not ellipsoidal, form of the three shells and the size of the 

 polar spines.) 



Dimensions. Diameter of the outer sphere 012, middle 0'06, inner 0'02 ; pores and spines of 

 the outer sh'ell O'Ol to 0-02, bars and porules 0'006 ; length of the major polar spine 015, of the 

 minor 0'05, breadth 0'04. 



Habitat. South Pacific, Station 285, depth 2375 fathoms. 



Genus 53.. Saturninus, 1 n. gen. 



Definition. S tylosphaerida with three concentric lattice-spheres and two equal 

 opposite spines, connected at the distal end by a circular or elliptical ring. 



The genus Saturninus differs from the similar Saturnulus by the triplication of the 

 spherical lattice-shell ; the inner shell is enclosed in the central capsule, whilst both the 

 others lie outside it. 



1. Saturninus triplex, n, sp. 



Eadial proportion of the three spheres = 4:3:1. Inner cortical shell with regular, circular 

 pores, of the same breadth as the bars, sixteen to eighteen on the half equator ; outer cortical 

 shell connected with the inner by numerous bristle-like radial spines, network very delicate, 

 cobweb-shaped, with irregular polygonal meshes. Ring elliptical, two and a half times as broad 

 as the outer shell. 



Dimensions. Diameter of the inner sphere 0'03, middle 0'09, outer 012 ; pores and bars of the 

 middle shell 0'004 ; major axis of the elliptical ring 0'3, minor 0'25 ; thickness of the ring and 

 the axial beams O'OOS. 



Habitat. Central Pacific; Station 272, surface; 



Subfamily CROMYOSTYLIDA, Haeckel, L881, Prodromus, pp. 449, 453. 



Definition. S tylosphserida with four concentric spherical lattice-shells (two 

 medullary and two cortical). 



Genus 54. Stylocromyum? Haeckel, 1881, Prodromus, p. 453. 



Definition. S tylosphserida with four concentric lattice-spheres and two free 

 spines of equal size and similar form. 



1 Saturninus^ Similar to Saturnus, with a ring. 



2 Stylocromyum= Onion with styles ; 



