142 THE VOYAGE OF H.M.S. CHALLENGEE. 



4. Satur nidus planetes, n. sjx (PL 16, fig. 17). 



Cortical shell smooth, twice as broad as the medullary shell, with regular, circular pores, of the same 

 breadth as the bars ; sixteen to eighteen on the half equator. Eiug elliptical, smooth, with strong 

 prominent edges, constricted at the poles of the minor axis, its major diameter three times as gi-eat 

 as that of the outer sphere. 



Dimensions. — Diameter of the outer sphere 0-08, pores and bars 0-005 ; inner sphere 0-035 ; 

 major axis of the ring 0-25, minor axis 0-2 ; thickness of the ring and the axial beams 0-012. 



Halitat. — Indian Ocean, Sunda Strait, Eabbe ; Station 200, surface. 



Subfamily Amphistylida, Haeckel, 1881, Prodromus, pp. 449, 452. 

 Definition. — S t y 1 o s p h as r i d a with three concentric spherical lattice-shells. 



Genus 51. Amphisphcera, Haeckel,^ 1881, Prodromus, p. 452. 



Df^HiiiOH.— S t y lospliEerida Avith three conceutric lattice-sj)lieres and two free 

 spines of equal size and similar form. 



The genus Amphisphoira difiers from its probable ancestral form, StylosphcEra, in 

 the triple spherical lattice-shell. Commonly two of these lie within the central capsule 

 (medullary shell), whilst the third lies outside it (cortical shell). But sometimes this 

 order is inverted, the cortical shell being double, the medullary shell simple ; and perhaps 

 these forms may better represent a peculiar genus, Amp>hisp)hcBridium. 



Subgenus 1. Amphisplmrantha, Haeckel. 



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

 surface smooth or a little rough, without spines or thorns. 



1. Ampjhispli(Bra neptunus, n. sp. 



Eadial proportion of the three concentric sjiheres = 4 : 2 : 1. Cortical shell thick walled, 

 smooth, with regular, circular, hexagonally framed pores, of the same breadth as the bars ; twelve to 

 fifteen on the half equator. Polar spines three-sided pyramidal, with strong prominent edges, about 

 as long as the radius of the outer shell, half as broad at the base. (Similar to Stylatradus ncjjtunus, 

 PI. 17, fig. 6, but differs in the purely spherical form of the three concentric shells and the 

 regular form of the network and of the polar spines.) 



Dimensions. — Diameter of the outer shell 0'16, middle shell 0-08, inner shell 0-04 ; pores and 

 bars of the cortical shell 0008 ; length of the polar spines O'OS, basal breadth 004. 



Habitat. — Pacific, central area. Station 271, depth 2425 fathoms. 



Ampliigph(era = ^\A\CTe with spines on both poles ; oifiipl, ctfoui^x. 



