64 THE VOYAGE OF H.M.S. CHALLENGER. 
rounded angle a single, short, cylindrical, tapering, sharply pointed spine, about the same 
size as the supero-marginal spine, directed at an angle outward and towards the extremity. 
The surface of the plate is covered with short papilliform granules, similar to those on the 
supero-marginal plates, which, however, become slightly larger and more widely spaced on 
the median part of the actinal area. They are crowded at the adoral and aboral margins, 
and a few at the base of the lateral spine are definitely spiniform. All are invested with 
delicate membrane. 
The adambulacral plates are long and narrow, and their length is such that they 
frequently appear to be correspondent to the infero- marginal plates; but careful exa- 
mination soon shows that this is merely deceptive. The furrow margin is straight. The 
armature consists of :—(1.) A furrow series of ten small, moderately elongate spinelets, 
slightly curved, with convexity towards the furrow, compressed laterally, and of nearly 
uniform breadth throughout, the tip being rounded, and their character is in consequence 
decidedly lamelliform. The outer spine at each extremity of the series is rather smaller 
than the others, which are subequal, and measure about 2°25 mm. in length, or slightly 
more on the innermost plates of the ray. The spines stand parallel and touch one another, 
forming a straight compact comb, and are invested with membrane. (2.) On the actinal 
surface of the plate, and immediately behind the furrow series, is a parallel series of five 
or six short, cylindrical, papilliform spinelets, shorter than the furrow series and rather 
wide apart; and external to this series, or sometimes forming one of it, is a cylindrical 
and very slightly tapering spinelet about 4 mm. in length, sometimes even a trifle more— 
consequently a very conspicuous feature in the armature. Its position is generally rather 
nearer the aboral end than midway on the plate. There are seven or eight very small, 
equal, papilliform spinelets along the outer margin of the plate, and sometimes an incom- 
plete series between this outer series and the series next the furrow spines. All the small 
spinelets, however, upon the actinal surface of the plate, are more or less irregular in their 
disposition, and this is especially noticeable in the inner part of the ray. No pedicellarize 
are present ; the surface of the plate is covered with membrane, and each of the papille 
is also thinly invested. 
The mouth-plates are large, and the united pair are convex actinally and extend pro- 
minently towards the actinostome. Their armature consists of a marginal series of fifteen 
or sixteen short spinelets on each plate, similar in character to the furrow series on the 
adambulacral plates, but which become more cylindrical and papilliform on the outer part 
of the series. One or two of the innermost mouth-spines are a little longer than the rest, 
and these decrease slightly as they recede from the mouth. The actinal surface of the 
plate is covered with numerous, short, papilliform spinelets, amongst which no order of 
arrangement is discernible; they are subequal in length, excepting about four at the 
extreme inner end of the mouth-angle, immediately behind the marginal series, to 
which they are nearly equal in length; and a second series of four or five behind these, 
