REPORT ON THE ASTEROIDEA. 161 
‘The mouth-plates are large, prominent, and elevated along the line of suture; the 
junction is imperfect, and the adoral extremities of the plates being widely open expose 
the odontophore. Their armature consists of six to eight mouth-spines on each plate, 
which are short, compressed, and pointed. The innermost one on each side is larger 
and longer than the rest, and is directed towards the actinostome; the lateral ones 
stand in the furrow and interlock with the corresponding denticles of the neigh- 
bouring mouth-angle. A number (varying from six to twelve) of small granule-like 
tubercles are present on the actinal surface of each plate ; two, which are slightly largest, 
stand near the inner third of the plate, whilst the remainder are confined to the aboral 
half of the plate, and are sometimes arranged in two or three lines, and sometimes 
irregularly. It seems scarcely possible to rank these as secondary mouth-spines ; and 
yet there can be little doubt that they are rudimentary or aborted representatives of 
these appendages, 
The actinal interradial areas are triangular in outline, and covered with a regular 
plating of hexagonal, imbricating, scale-like intermediate plates arranged in columnar 
series extending from the margin to the furrow, parallel to the median interradial 
line. The plates are broader than long, the disproportion increasing as they approach 
the margin; they bear a few (three to five) small, widely spaced, irregularly disposed 
granules, some plates here and there having none. 
Colour in alcohol, greyish white on the margins and actinal area ; abactinal membrane 
bluish grey, with touches of light brown near the margin of the area and occasionally 
on the groups of paxillze round the centre of the disk. 
Locality.—Station 299. Off the western coast of South America, between Valparaiso 
and the Island of Juan Fernandez.. December 14, 1875. Lat. 33° 31’ 0” S., long. 74° 
43'0” W. Depth 2160 fathoms. Blue mud. Bottom temperature 35°°2 Fahr. ; surface 
temperature 62°°0 Fahr. 
Remarks.—Hyphalaster diadematus is distinguished from the other members of 
the genus by the prominent groups of larger paxilla on the abactinal area of the disk 
(the character from which the name is derived), and by the presence of five cribriform 
organs. 
The example of this species, which is figured on Pl. XXI., did not come into my hands 
until some time after the preliminary notice’ of this group had been published. It 
was one of the two species which had been drawn under the direction of the late 
Sir Wyville Thomson before the collection was entrusted to me, and after his death 
the specimens had been mislaid amongst other things, and were lost sight of for 
some time. 
The type which has been described is larger and differs slightly in several respects, 
but I see no reason to doubt for a moment that the two examples belong to the same 
1 Journ. Linn. Soc. Lond. (Zool.), 1883, vol. xvii. p. 237. 
(ZOOL, CHALL. EXP.—PART LI.—1887.)| 21 
