42 THE VOYAGE OF H.M.S. CHALLENGER. 
furrow series of ten to twelve small, delicate, cylindrical spinelets, their delicacy giving them 
an elongate appearance. These are situated on the margin of the angular projection, andradiate 
slightly apart, the length of the spines diminishing as they recede from the apex of the angle. 
Two or three still smaller spines form a continuation of the marginal series on each side 
on the surface of the plate. (2.) On the actinal surface of the plate are a number of small 
spinelets, similar in size and character to the furrow series. An oblique line of three to 
five, running subparallel to the adoral side of the angular prominence, is nearly always 
definitely formed, and sometimes a second line of fewer spines is discernible, converging 
towards the inner extremity of this line, with sometimes one or more spines in the 
included area, but usually the spines additional to the oblique line first mentioned are 
more or less grouped and irregular in their disposition. All these spines diminish in 
length as they recede from the furrow. Several of the adambulacral plates on the inner 
half of the ray bear at their junction with the marginal plates one of the large pedicel- 
larian apparatus about to be described presently. 
The mouth-plates are broad and conspicuous, but only slightly convex. The inner free 
margin of the united pair is subcircular in outline or even subparaboloid. The armature 
consists of ten small, slightly compressed, obtusely rounded spinelets, on each plate. The 
innermost one is much the longest and most robust, and is abruptly pointed; the other 
spinelets decrease as they recede from the mouth. There is consequently a pair of larger 
mouth-spines at each mouth-angle directed horizontally over the actinostome parallel 
to one another, the five pairs meeting at the centre of the orifice. The actinal sur- 
face of the plate is covered with a number of very small, uniform, delicate, thornlike 
papilliform spinelets, rather widely spaced, amongst which no order of arrangement is 
distinguishable. 
The actinal intermediate (ventral) plates are not more than eight to ten in number in 
each interradial area, and they bear a peculiar pedicellarian apparatus. This is situated on 
the suture between two laterally adjacent plates, and consists of five or six short tapering 
compressed spinelets borne on each plate on the margin of a semicircular cavity, over which 
they are directed so as to meet and interlock at their tips with the corresponding series of 
the neighbouring plate. The outline of the apparatus is suboval, and the cavity contains in 
most cases a pulpy mass, probably foreion matter. There are five of the organs in each of 
the interradial areas, the median one and the next adjacent on each side being the largest ; 
and from three to six similar organs may be present on isolated adambulacral plates on 
each side of a ray, as noticed above. A few pseudo-pedicellarive of similar appearance, 
formed by the modified spinelets of adjacent paxillee, occur occasionally on the paxillar 
area of the abactinal surface. 
The anal aperture is subcentral and distinct, and surrounded by a circlet of slightly 
larger spinelets. 
The papulze are confined to a limited area at the base of each ray, but I am unable to 
