77.) 
REPORT ON THE ASTEROIDEA, 337 
definite border to the actinal area, to which they are in reality confined. Their 
breadth is greater than their length, and they present a prominent narrow keel, which 
is closely crowded with small spinelets similar to those on the paxille. There are 
thus deep channels between adjacent plates. 
The adambulacral plates are small and rather widely spaced. Their armature consists 
of a more or less compact wedge-shaped group of small, cylindrical, more or less tapering, 
subequal spinelets. Three to five stand on the furrow margin and form a very acute 
angle, one spinelet being at the apex ; one or two similar and equal-sized spines are placed 
on the actinal surface of the plate within the area enclosed by the marginal series; 
and behind these, on the outer part of the actinal surface of the plate, may be two or 
three smaller and irregularly placed spinelets. 
The mouth-plates, which are comparatively large and elongate, are slightly prominent 
actinally, with a low convexity. Their whole surface is covered with short spinelets 
moderately spaced, which increase in length as they approach the inner end of the 
plates. From seven to ten spinelets stand in the marginal series, the innermost 
similar to, but slightly larger than, the furrow spinelets on the adambulacral plates ; 
the other spinelets on the mouth-plates are irregular in number and position, and 
the whole structure has a very echinulate appearance. 
The actinal interradial areas are well developed, and are occupied by thin imbricating 
plates, which form isolated columns arranged in regular transverse and slightly oblique 
lines between the adambulacral plates and the marginal plates. All are overlaid with 
a uniform continuous membrane, through which the plates are not individually distin- 
guishable, or can only be traced here and there. The intermediate plates extend far 
along the ray, but do not reach the tip; the numbers in the transverse columns 
diminishing gradually as they proceed outward. From seven to nine plates may be 
counted in the series adjacent to the median interradial line. Each intermediate 
plate bears on an elevation on its actinal surface a paxilliform group of spinelets, 
which are larger and coarser than those on the abactinal paxille. The plates adjacent 
to the adambulacral plates have a distinctly elongate eminence and paxilla. 
In some examples these actinal paxille are much coarser and more compact than 
in others, and the central spinelets of the crown have a tendency to be more robust 
and prominent. Usually the spinelets are radiating and comparatively delicate. 
, The madreporiform body, which is large and conspicuous, is situated rather nearer 
the margin than midway on the interradial line. Its surface is slightly convex and 
often wrinkled or broken up, as if originally formed by the union of several plates. 
The striation furrows are very fine and radiate centrifugally, very little convolution 
being noticeable. 
The ambulacral tube-feet are large, with a moderately developed, rounded, button-like 
knob at the extremity. 
(ZOOL. CHATI.. EXP.—PART L1.—1888.) 43 
