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



Polar spines three-sided pyramidal, about as long as the axis of the outer sphere, one-fourth as broad 

 as its radius. (Similar to Xiphosphcera vesta, PI. 14, fig. 6.) 



Dimensions. Diameter of the outer shell 015, pores O'OOS to 0'015, bars 0'003 ; inner shell 0'05 ; 

 polar spines 012 long, 0'02 broad. 



Habitat. South Atlantic, Station 335, depth 1425 fathoms. 



Genus 49. Sphcerostylus,^ Haeckel, 1881, Prodromus, p. 451. 



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

 spines; of different size ox form. 



The genus Sphcerostylus differs from Stylosphcera in the different size or form of 

 the two polar spines, and therefore has the same relation to it that Xiphostylus bears 

 to Xiphosphcera. 



Subgenus 1. Sphcerostylantha, Haeckel. 



Definition. Pores of the cortical shell regular, of nearly equal size and similar 

 form ; surface smooth or a little rough, without thorns. 



1. Sphcerostylus liostylus, Haeckel. 



Stylosphcera liostylus, Ehrenberg, 1875, Abhandl. d. k. Akad. d. "Wiss. Berlin, Taf. xxv. fig. 2. 



Cortical shell thin walled, with rough surface, three times as broad as the medullary shell. 

 Pores of the cortical shell regular, circular, twice as broad as the bars ; ten to twelve on the half 

 equator. Polar spines cylindrical, as broad as one pore, with conical apex ; the minor spine about 

 as long as the axis of the outer shell, the major three to four times as long. 



Dimensions. Diameter of the outer sphere 012, pores 012, bars 0006 ; diameter of the inner 

 sphere 0~04 ; length of the major polar spine O-'S to 0"4, of the minor 01 to 015, breadth 0'012. 



Habitat. Fossil in the Barbados rocks. 



2. Sphcerostylus flexuosus, Haeckel. 



Stylosphaira flexuosa, Ehrenberg, 1875, Abhandl. d. k. Akad. d. Wiss. Berlin, Taf. xxv. fig. 5. 

 Cortical shell thick walled, with rough surface, three times as broad as the medullary shell. 

 Pores of the cortical shell regular circular, of the same breadth as the bars ; eight to ten on the 

 half equator. Polar spines cylindrical, S-like curved, irregular ; the minor scarcely as long as the 

 axis of the outer sphere, the major two to three times as long. (In the figure of Ehrenberg 

 the spines are broken off; I have found them myself constantly irregular and of unequal length, 

 sometimes with conical apex.) 



1 Spharoslylus = Sphere with styles ; <r@i, aru^os. 



