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



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

 aiajor 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 Xiphatrcictus glyptoclon, PL 17, 

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

 polar spines.) 



Dimensions. — Diameter of the outer sphere 012, middle O'OG, inner 01)2 ; pores and .spines of 

 the outer shell O'Ol to 0-02. bars and porules O'OOG ; length of the major polar spine 015, of the 

 minor 0-05, breadth 0-04. 



Eahitat. — South Pacific, Station 285, depth 2375 fathoms. 



Genus 53. SaturninKs} n. gen. 



Definition. — St yl ospliserida with three concentric lattice-spheres and two ecjual 

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



The genus Saturninns differs from the similar Saturnulus by the trijjlication of the 

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

 others lie outside it. 



1. Saturninns triplex, u, sp. 



Eadial proj^ortion 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 dehcate, 

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

 as the outer shell. 



Dimensions. — Diameter of the inner sphere O'Oo, 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 a.xial beams O'OOS. 



Habitat. — Central Pacific, Station 272, surface: 



Subfamily Cromyostylida, Haeckel, 1881, Prodromus, pp. 449, 453. 



Definition. — S t y losphasr id a with four concentric spherical lattice-shells (two 

 medullary and two cortical). 



Genus 54. Sti/locromi/ttm,^ Haeckel, 1881, Prodromus, p. 453. 



Dejinition. — S tylosph serid a with four concentric lattice-spheres and two free 

 spines of ecjual size and similar form. 



• Haturninus = Similai to Satunms, with a ring. 



- Stylocrormjum=Onion with styles ; arvKo;, x.^6,uvr,s. 



