1566 THE VOYAGE OF H.M.S. CHALLENGER. 



9. Distephanus sirius, Haeckel. 



Actiniseus sirius, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 68. 

 Didyocha sirms, Ehrenberg, 1854, Mikrogeol., Taf. xviii. fig. 59. 



Each pileated piece of the skeleton is a truncated six-sided pyramid, similar to that of 

 Distephanus sjMculuvi, but distinguished by the six broad, triangular, peripheral spines, which are 

 articulated and connected by a thin siliceous membrane (Hke a web-membrane) ; each spine has 

 three articulations (as in Bidyocha pentasterias). 



Dimensions. — Diameter of the basal ring 0'02, of the apical ring 0'005. 



Habitat. — Fossil in Tertiary rocks (Eichmond, Virginia), but also living in the Atlantic Ocean, 

 Gulf Stream, Fairiie Channel, John Murray, 1880. 



10. Distcphmius corona, n. sp. (PL 114, figs. 7—9). 



DidyocJui corona, Haeckel, 1881, Prodromus. 



Each pileated piece of the skeleton is a truncate six-sided pyramid, like that of Distephanus 

 speculum, but differing in the number (twenty-four) of teeth or spines. Six interradial ascending 

 beams connect the two horizontal rings between these, and six nearly vertical spines arise from the 

 perradial corners of the upper hexagonal ring. In the same meridional (perradial) plains six larger 

 spines descend downwards from the corners of the lower larger ring. Between these six descending 

 spines and the six ascending beams arise from the upper edge of the lower ring twelve shorter 

 teeth of unequal size (the right tooth in each pentagonal lateral mesh being smaller, and directed 

 upwards, the left tooth being larger and directed nearly liorizontally outwards). The lower ring 

 is nearly dodecagonal. 



Dimensions. — Diameter of the basal ring 0'025 to 0'03, of the apical ring 0'012 to 0'02. 



Habitat. — North-west Pacific, Sea of Japan, Station 231, depth 2250 fathoms. 



11. Distephanus octonarius, Haeckel. 



Didyocha odonaria, Ehrenberg, 1844, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, p. 201. 

 Didyocha polyactis, Ehrenberg, 1844, loc. cit., p. 80 ; Mikrogeol, 1854, Taf. xxii. fig.' 50. 

 Dicfyocha septenaria, Ehrenberg, 1844, loe. cit., p. 80; Mikrogeol, 1854, Tat xxi. fig. 45. 



Each pileate piece of the skeleton is a truncated eight-sided pyramid, composed of two regular 

 octagonal rings, which lie in parallel plains and are connected by eight radial beams. From the 

 eight outer corners of the lower ring (or from the eight interradial meshes, between the eight 

 perradial beams) start eight basal centrifugal spines. (This species is similar to Distephanus speculum, 

 but has eight beams instead of six. In single pieces the number of the beams and meshes varies 

 between seven and nine, the constant number being eight.) A seven -rayed variety is Didyocha 

 septenaria {loc. cit.), a nine-rayed Didyocha p)olyactis. 



Dimensions. — Diameter of the basal ring 0-02 to 0-03, of the apical ring Q-Ql to 0-015. 



Habitat. — Fossil in Tertiary rocks (Tripel and Marne from Caltanisetta, Sicily; Oran, Africa); 

 living in the depths of the Atlantic, Station 348, and Pacific, Station 270, &c. 



