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 149b. Off Royal Sound, Kcrguelen Island. January 17, 1874. 

 Depth 25 fathoms. Volcanic mud. Surface temperature 40 o, 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 Perhnaster 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 Perhnaster fuscus approaches the 

 character of some of the Southern species of Cribrclla. 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. Perhnaster densus, n. sp. (PI. XCVII. figs. 1 and 2 ; PI. XCVIII. figs. 11 and 12). 



Pays five. R = 51 mm. ; 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 paxillos. Between the plates 

 papulae 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. 



