REPORT ON THE ASTEROIDEA. 53 
extremity where they become quite microscopic. ‘The rest of the plate is covered with 
very minute, uniform, thorn-like, or spiniform granules, widely spaced. 
The infero-marginal plates are correspondent to the superior series, and similar in 
every respect ; but they extend much further on the actinal surface than the superior series 
do on the abactinal surface, and are distinctly tumid in the actinal aspect ; their breadth 
up to the middle of the ray is greater than their length, and on the inner part at least of 
the ray the two series alternate instead of being directly superposed. ach plate bears a 
single conical spine, similar to that on the supero-marginal series, directed horizontally and 
very slightly outwards. The fourth or fifth spine from the median interradial line is the 
longest, and measures about 3 mm. ; outward from this the length diminishes gradually, 
but to a less degree than in the superior series; on the outer half of the ray they are 
consequently longer than the companion series, and are distinctly visible up to the 
extremity although very small—less than one millimetre in length at the tip. Midway 
between the lateral spine above described and the inner margin of the plate is a small 
spinelet similar in character but one third the size; this disappears, however, on the outer 
part of the ray. The rest of the plate is covered with minute, widely spaced, thorn-like 
spinelets, rather longer and more spine-like than the covering of the supero-marginal 
plates ; but their isolation and paucity are remarkable. 
The adambulacral plates form conspicuous semicircular or angular projections into the 
furrow. Their armature consists of :—(1.) A furrow series of six to eight small, cylin- 
drical, slightly tapering, blunt or roundly pointed spinelets, the outer one on each side 
being much shorter than the rest. These spinelets are covered with a delicate tissue, and 
are arranged on the margin of the semicircular projection. When the furrow is contracted 
and the spines are directed vertically to the plane of the actinal surface, they form a 
subpalmate group with a more or less acute angle into the furrow ; the opposite series on 
the two sides of the furrow touching one another, and entirely separating each pair of 
tube-feet from their neighbouring pairs. (2.) On the actinal surface of the plate is a 
single, robust, conical, and sharply-pointed spine similar in character to the lateral spines, 
and about half the length, and behind this are usually two or three small, short, thorn-like 
spinelets ; but no other spinelets or granules are present on the plate. 
The mouth-plates are large, tumid actinally, and the united pair are as broad as long. 
Each plate bears on its free margin an armature of seven spines, which increase in length 
as they proceed inwards, the innermost being twice the length of the outermost, which 
are not greater than the smallest spines of the adambulacral armature. The inner- 
most pair stand parallel, and are directed towards the centre of the actinostome, the 
succeeding spines being parallel or only radiating very slightly at the outer part of the 
series. On the surface of the plates there are three small spinelets in a line with the 
median suture, the innermost the longest, and the outermost the smallest ; and in the 
space between the outermost spine of this series and the free marginal series of spines is a 
tolerably robust, conical, and pointed spine longer than the rest, the representative of the 
