I 



EEPOKT ON THE ASTEKOIDEA. 97 



34° 8' 0" S., long. 152° 0' 0" E. Depth 950 fathoms. Green mud. Bottom tempera- 

 ture 36 0, 5 Fahr. ; surface temperature G9 0, 5 Fahr. 



Remarks. — This is a very characteristic form, and distinguished from all other species 

 by the small marginal plates, the well-developed infero-marginal spines, the conical 

 tubercle on the supero-marginal plates, the conically-pointed granulation of the marginal 

 plates, and the simple radiating paxillse. 



5. Plutonaster notatus, n. sp. (PL XIV. figs. 6 and 7 ; PI. XV. figs. 5 and 6). 



Kays five. K = 31 '5 mm. ; r = 10 - 75 mm. R < or. Breadth of a ray at the fifth 

 supero-marginal plate, 5*5 mm. ; midway along the ray, 4*5 mm. 



Rays short, very narrow, and slightly tapering ; the wide and open interbrachial arcs 

 emphasising their narrowness, as well as the pentagonal character of the disk from whence 

 they proceed. Nearly square in section, with the angles slightly rounded. Disk com- 

 paratively large. Abactinal surface of the disk slightly convex and inflated ; that of the 

 rays being flat. Actinal surface of the disk very slightly convex, subplane along the 

 rays. 



The abactinal surface of the disk and rays is covered with numerous small paxillse, 

 composed of short, cylindrical, obtusely tipped, equal spinelets, standing upright and 

 forming compact little groups of uniform height, with seven to fifteen spinelets in each, 

 two to four being central and usually slightly more robust than the others. Though 

 crowded, the paxillse are so spaced that each remains distinct ; upon the central area of 

 the disk no order of arrangement is discernible, but near the marginal plates they are dis- 

 posed in lineal series running towards the marginal plates. The series on each side of 

 the median interradial line are parallel thereto ; and as each succeeding sexies converges 

 slightly, their position at the base of the ray is obliquely transverse to its axis ; in other 

 words, if the lines of these lineal series were produced, they would meet at a common point 

 outside the margin in the prolongation of the median interradial line. This arrangement 

 does not extend beyond the base of the rays ; outward along the rays the paxillse present 

 no definite order of arrangement, nor yet upon the median radial line throughout, nor 

 on the whole central area of the disk, as above noticed. No pedicellarias are present. 



The supero-marginal plates, twenty-two to twenty-four in number from the median 

 interradial line to the extremity, are small, but form a distinct and regular border to the 

 disk and rays. When viewed from above their breadth on the abactinal surface is slightly 

 greater than their length ; and when viewed laterally the height is subequal to the length 

 along the greater portion of the ray, but increases in the interbrachial arc, where the 

 plates have a smaller abactinal bending. Midway along the ray, the breadth of the supero- 

 marginal plates is nearly as great as the width of the paxillar area. The union of the 

 abactinal and lateral planes of the plates is well rounded. The supero-marginal plates 

 bear no spines, but their surface is covered with tolerably large, uniform, hemispherical, 



(ZOOL. CHALL. EXP. — PART LI. — 1887.) 13 



