156 THE VOYAGE OF H.M.S. CHALLENGER. 
Chorology of the Genus Hyphalaster. 
a, Geographical distribution -— 
Arantic: Two species (fide Perrier). 
Hyphalaster antonii and Hyphalaster parfoate. 
Pactric: Three species between the parallels of 40° N. and 40° 8. 
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. 
SourHErN Ocean: One species between the parallels of 50° and 60° S. 
Hyphalaster planus near the meridian of 110° E. 
8. 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 Radiolarian ooze. 
Chorological Synopsis of the Species herein described. 
Ocean. Range in Fathoms. | Nature of the Sea-bottom. 
Hyphalaster diadematus . ; . | Pacific, 2160 Blue mud. 
Hyphalaster hyalinus ; 2 ~ |) -Bacifie: 2750 Radiolarian ooze. 
Hyphalaster inermis . . : , Pacific. 1875 Blue mud. 
Hyphalaster planus . : : : | Southern Ocean. 1950 Diatom ooze. 
1. Hyphalaster hyalinus, Sladen (Pl. XXVI. figs. 1-6; Pl. XXVIII. figs. 13-16). 
Hyphalaster hyalinus, Sladen, 1883, Journ. Linn. Soc. Lond. (Zool.), vol. xvii. p. 235. 
Rays five R=20mm.;7r=10mm. R=27. 
Rays 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. 
