552 THE VOYAGE OF H.M.S. CHALLENGER. 
Colour in alcohol, a dark purplish brown on the abactinal surface. The numerous 
spinelet-tips are nearly white. The actinal surface is much lighter than the abactinal. 
Localities.—Station 1498. Off Royal Sound, Kerguelen Island. January 17, 1874. 
Depth 25 fathoms. Volcanic mud. Surface temperature 40°°5 Fahr. 
Station 151. Off Heard Island. February 7, 1874. Lat. 52° 59’ 30” S., long. 73° 
33/30” E. Depth 75 fathoms. Volcanic mud. Surface temperature 36°:2 Fahr. 
Remarks.—This species may be distinguished from Perknaster densus by the general 
form, by the colour, by the character of the spinulation, and by the armature of the 
adambulacral plates. In the last-mentioned particular Perknaster fuscus approaches the 
character of some of the Southern species of Cribrella, but the present form could not be 
mistaken for any of these. 
The example dredged off Heard Island is somewhat longer in the rays than those 
from Kerguelen. 
2. Perknaster densus, n. sp. (Pl. XCVIL figs. 1 and 2; Pl. XCVIII. figs. 11 and 12). 
Rays five. R=51mm.; r=16 mm. R>3,r. Breadth of a ray at the base, about 
18 mm. ; breadth about midway between the disk and the extremity, 7°5 mm. 
Disk large and inflated. Rays subcylindrical, broad at the base, and tapering gradually 
up to the extremity, which is obtusely pointed. Interbrachial arcs distinctly angular. 
Slight depressions feebly defined are present in the median interradial lines on the 
abactinal surface of the disk. The actinal surface of the disk is concave. 
The whole abactinal and lateral surfaces, extending up to the adambulacral plates, are 
covered with small plates which bear small compact groups of short, obtusely rounded, 
equal spinelets; the whole resembling closely crowded paxille. Between the plates 
papulze are interspersed, but are rarely visible superficially in consequence of the crowding 
of the spinulation. No order of arrangement whatever is discernible in the plates either 
on the abactinal or actinal areas, and no traces of the representatives of marginal plates 
can be detected. 
The armature of the adambulacral plates consists of about three pairs of obliquely 
placed spinelets, the whole forming a transverse double series of spinelets. The innermost 
pair are larger than the others, and thickly skin-covered, which gives them a robust and 
often a subprismatic appearance. ‘The outer spinelets are shorter and more cylindrical, and 
merge into the general spinulation of the actinal surface. The obliquity of the position of 
the pairs causes one of the spinelets of the innermost pair to be more prominent into 
the furrow than its companion. No small inner spinelet is present high up in the furrow, 
as in Cribrella. 
The madreporiform body, which is rather large, is situated about midway between 
the centre of the disk and the margin, and its surface is marked with fine convoluted 
striations. 
