156 



TILE VOYAGE OF H.M.S. CHALLENGER. - 



CJwrology of the Genus Hyphalaster. 



a. Geographical distribution : — 



Atlantic : Two species {fide Perrier). 



Hyphalaster antonii and Hyphalaster parfaiti. 



Pacific : Three species between the parallels of 40° N. and 40° S. 



Hyphalaster inermis off the coast of Japan, south of Kawatsu. 

 Hyphalaster hyalinus in the Mid-Pacific, due north of the Society 

 Islands and due west of the Marquesas Islands. Hyphalaster 

 diadematus off the west coast of South America, between Valparaiso 

 and the Island of Juan Fernandez. 



Southern Ocean : One species between the parallels of 50° and 60° S. 

 Hyphalaster planus near the meridian of 110° E. 



/S. Bathymetrical range: 1875 fathoms to 2750 fathoms. 



All the species are confined to the Abyssal zone, and two {Hyphalaster 

 diadematus and Hyphalaster hyalinus) to depths greater than 2000 

 fathoms. 



y. Nature of the Sea-bottom: Two species, Hyphalaster diadematus and Hyphalaster 

 inermis, are found on Blue mud. Hyphalaster planus on Diatom ooze. 

 Hyphalaster hyalinus on Eadiolarian ooze. 



Chorological Synopsis of the Species herein described. 



1. Hyphalaster hyalinus, Sladen (PI. XXVI. figs. 1-6; PI. XXVIII. figs. 13-16). 



Hyphalaster hyalinus, Sladen, 1883, Joiirn. Linn. Soc. Lond. (ZooL), vol. xvii. p. 235. 



Pays five. E = 20 mm. ; r = 1 mm. R = 2r. 



Pays short, small, rounded, and of uniform thickness throughout. The disk, although 

 not high, is more or less inflated ; the minor radius is in the proportion of 50 per cent. 

 The interbrachial arcs are of great width, the curve being almost lost in the straightness 

 of the side of the pentagonal disk. 



