ASTEKOIDEA OF H.M.S. ' CHALLENGEIl ' EXPEDITIOJNT. 235 



IlrPHALASTEB HTALINUS, 11. Sp. 



Rays five, short, small, rounded, and of uniform thickness 

 throughout. Interbrachial angles of great width, the curve 

 being almost lost in the straightness of the side of the pentagonal 

 disk. The lesser radius is in the proportion of 50 per cent. ; 

 i2 = 20 millim., r = 10 millim. The disk, although not high, is 

 more or less inflated. Dorsal area covered wiih a thin and 

 almost transparent membrane, which is indurated with a great 

 number of spiculate spinelets or pseudo-paxillse ; these consist 

 of a circular scale-like base, from the centre of which a spine-like 

 process rises vertically, and this may be divided into two, three, 

 or four equal spinelets, the latter number being the most 

 general in the centre of the disk and those with one spinelet 

 near the margin. The spinelets are moderately robust, obtuse, 

 all united at the base, and radiating apart very slightly, have 

 more or less the ajipearance of imperfect paxillse ; whilst the 

 squamous basal plate is scarcely larger than the diameter of the 

 vertical sjDinous process. These pseudo-paxillse are rather crowded 

 in the immediate centre of the disk, but are elsewhere moderately 

 and uniformly well spaced. There are no papulae. The presence 

 of an actual anal aperture is doubtful. 



Marginal plates form a perpendicular wall of small but uniform 

 height; the upper margin of the superior series and the lower 

 margin of the inferior series are slightly bent inwards and form 

 bevelled edges. The supero-marginal plates are eight in number, 

 counting from the median interbrachial line, exclusive of the 

 terminal. The innermost plates are nearly twice as long as high, 

 and the outermost are higher than long. The two innermost 

 plates on either side of the median interbrachial suture each bear 

 a single, very minute, conical spiuelet near the upper margin 

 and directed horizontally. The two outermost supero-marginal 

 plates extend to the median dorsal line, where they join the 

 corresponding plates from the other side of the ray ; the two 

 next plates are separated by a narrow strip of dorsal membrane 

 with pseudo-paxillse ; and the remaining plates fall in the disk- 

 margin. The terminal plate is slightly tumid proximally and 

 tapers rapidly to a fine extremity, which is continued in a robust, 

 sharply pointed terminal spine. This spine, which is longer than 

 ^he plate, is placed in the median dot sal line of the ray, and is 

 directed outward and slightly upward from the horizontal; two 

 smaller spinelets, less than half the size of the above, are placed 



