154 THE VOYAGE OF H.M.S. CHALLENGER. 
adoral extremity of the margin, equal in length, stretching over the furrow, and radiating 
apart from one another; the third spinelet is slightly smaller, placed about midway on 
the margin of the adambulacral plate, and is directed in the same direction as the aboral 
of the two spines. The spinelets are invested with a very fine membrane, which is con- 
tinuous at their bases, and the spinelets of one side of the furrow interlock with those 
from the other. Behind the furrow series, at the adoral end of the plate, and standing on 
the prominent swelling, away from the margin of the furrow, a small conical spinelet rises 
perpendicularly from the surface of the plate; and this becomes more or less rudimentary 
as it proceeds along the free portion of the ray. 
The mouth-plates, which are large, prominent, and not united along the median 
suture, have a peculiar appearance, resembling the shape of a coulter in a marked degree. 
Their armature consists of five or six mouth-spines placed side by side along the lateral 
margin of the plate, similar in length and character to the spinelets constituting the 
armature of the adambulacral plates, and these interlock with the corresponding series of 
spines of the neighbouring mouth-angle. About three small, aborted, tubercular spinelets 
situated on the surface of the plate are probably the representatives of secondary mouth- 
spines. The plates of each pair of mouth-plates are wide apart, and being unclosed at 
their aboral extremity, expose the odontophore. 
The actinal interradial areas are rather large and triangular, covered with squamous 
intermediate plates, which are narrow, elongate, imbricating, and regularly arranged in 
columns on the outer half of the area, but become larger, broader, subrotund, and 
irregular as they approach the mouth-angle. The plates are smooth, without granules, 
and the investing membrane is of such remarkable thinness that its presence is almost 
questionable. 
Colour in alcohol, grey, with a slightly brownish shade over the paxillar area. 
Locality—Station 224, In the neighbourhood of the Caroline Islands, 100 miles 
north of the Admiralty Islands. March 21, 1875. Lat. 7° 45’ 0” N., long. 144° 20’ 0” E. 
Depth 1850 fathoms. Globigerina ooze. Bottom temperature 35°°4 Fahr.; surface 
temperature 81°°2 Fahr. 
Genus Hyphalaster, Sladen. 
Hyphalaster, Sladen, Journ, Linn. Soc. Lond. (Zool.), 1883, vol. xvii. p. 2344 
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 radial line, 
and enclosing the ray. 
Abactinal membrane with pseudo-paxille ; simple spinelets also present in some forms 
on the outer part of the area only. A conical epiproctal protuberance may be more or 
