REPORT ON THE ASTEROIDEA. 369 
spinelets occurs, which in any way indicates the outlines of the underlying plates of the 
abactinal floor; and the only break in this perfectly uniform covering consists of a 
number of most minute channel-lines which run irregularly here and there amongst the 
spinelets, the only one of these maintained with any regularity being a long straight 
channel, similar in breadth to all the others, extending along the median interradial line. 
The anal aperture is subcentral and distinct, and is surrounded by shghtly larger spinelets. 
The madreporiform body is very small, round, and with numerous strie. It is situated 
rather nearer to the margin than midway to the centre of the disk, and the surrounding 
portion of the test is slightly prominent. 
The actinal interradial areas are extensive, and have their outer margin conspicuously 
festooned by the infero-marginal plates. 
The infero-marginal plates are eight or nine in number, counting from the median 
interradial line to the extremity of the ray; their outer margin has a rounded 
contour and bears a group of eight to twelve spinelets, rather larger and more robust than 
those of the abactinal area above described. The plates are entirely covered with spine- 
lets—the part which falls in the side of the ray with spinelets similar to those on the 
abactinal area, and the actinal portion with spines similar to those on the actinal area. 
When the starfish is viewed in profile, the marginal plates are seen to be clearly marked 
out by vertical furrows as well as by their prominent tumidity ; but the junction of the 
infero-marginal plates with the supero-marginal plates, or indeed the presence of these 
latter at all, is indiscernible to superficial observation. Seen on the actinal side the 
marginal plates are clearly defined by well-marked channels or furrows, which run in 
oblique lines from the margin up to the adambulacral plates. The furrows are almost 
regularly parallel, hence the areas or columns they define are of nearly uniform breadth 
throughout. Consequent on their oblique direction a triangular space occurs in the 
median interradial line in the outer portion of the area, which is not conformable to the 
arrangement above described, the channels which traverse it converging towards the apex 
of the triangular space, a short distance removed from the margin of the disk. 
The whole actinal area is covered with small, almost spicular, spinelets which are 
short, sharply pointed, and with their bases buried in membrane. ‘The spinelets are all 
nearly uniform in size, rather widely spaced, and are directed outward, almost horizontally, 
the angle at which they stand to the actinal surface being very small. 
The ambulacral furrows are narrow and almost uniform in breadth throughout. ‘The 
adambulacral plates are broader than long. ‘Their armature consists of from five to eight 
spines, which form (1.) a regular inner or furrow series which arches over and almost conceals 
the ambulacral tube-feet ; and (2.) three subregular outer rows more or less clearly defined. 
The following is the arrangement of the spinelets on the plates. Of the inner or furrow 
series there are two spines on each plate, which stand side by side and slightly oblique, 
especially towards the end of the ray. These two spines are regular throughout the ray 
(ZOOL, CHALL. EXP.—PART LI.—1888.) 47 
