231 MR. W. PERCY SLADBN ON THE 



plates are smootli; without granules, and the investing membrane 

 is of such remarkable thinness that its presence is almost ques- 

 tionable. 



Colour, in alcohol, gi^ey, with a slightly brownish shade over 

 the paxillar area. 



Station 224. Lat. 7° 45' N., long. 144° 20' E. Depth 1850 

 fms. ; bottom temperature 1°'3 C. ; Glohigerina-ooze. 



Hyphalaster, n. gen. 



Rays five, short, incapable of being reverted. Disk more or less 

 depressed and pentagonal. Supero-marginal plates devoid of spines, 

 sometimes uniting in the median dorsal line and enclosing the ray. Ab- 

 actinal membrane with pseudo-paxillas ; simple spinelets also present in 

 some forms on the outer part of the area only. A conical epiproctal pro- 

 tuberance may be more or less defined in the centre of the disk, similar to 

 that present in some species of Asiropecten, but not developing the 

 tubular structure of this appendage found in Porcellanaster. Actinal 

 interradial areas extensive, paved with numerous thin plates arranged in 

 regular columns and imbricating. Arabulacral furrows narrow and con- 

 cealed. Ambulacral spines short, compressed, three to five in number, 

 usually forming a kind of fan or independent series on each plate. Cri- 

 briform organs five to seven m number in each angle. 



Synopsis of Species herein descrihed. 



A. Five cribriform organs in each angle. Dorsal area 



with prominent groups of paxillte diadematus. 



B. Seven cribriform organs hi each angle. No prominent 



groups of paxillse on the dorsal area. 

 t Supero-marginal plates meet in the median line. Cri- 

 briform organs very narrow. Secondary row of granules 

 behind the ambulacral spines aborted or absent. 

 * Disk with very imperfect pseudo-paxillfe. Two 

 innermost supero-marginal plates on each side of the 

 median interbrachial line with small spinelets. 

 ' Mouth-plates with secondary moutb-sj^ines. Body- 



fi-ame very thin and delicate hyalinv.s. 



** Disk with fully developed paxillae. No spinelets on 

 supero-marginal plates. No secondary mouth- 

 spines. Body-frame robust and rigid inermis. 



tt Supero-marginal plates not united in the median line. 

 A series of small secondary granules behind the 

 ambulacral spines. Cribriform organs very broad 

 and expanded planus. 



