34 THE VOYAGE OF H.M.S. CHALLENGER. 
rounded margin of the ray and is directed outward at an angle of about 45° to the plane 
of the abactinal surface. The surface of the plate is entirely covered with small, equal, 
papilliform granules, or minute stunted clavate spinelets; and occasionally one or two 
immediately below the conical spine are longer, more definitely spine-like, and tapering. 
The infero-marginal plates alternate with the superior series, and both their height and 
their breadth are greater than their length. Hach plate bears a short, robust, conical but 
often truncate lateral spine, which is, however, longer and more robust than the spine 
on the supero-marginal plates ; and this is followed by two or three, or even more, smaller 
tapering and pointed spinelets ; the character of the whole spinulation along the median 
part of the plate being definitely spine-like, the spinelets decreasing in size as they recede 
from the lateral spine and approach the inner end of the plate; two or sometimes 
three irregular series may be frequently defined, one series, however, being larger than 
the others. The rest of the surface of the plate is covered with small papilliform 
spinelets, which become more crowded, delicate, and cilia-like along the margins of the 
transverse sutures. 
The adambulacral plates are broad and form prominent angular projections into the 
furrow. Their armature consists of :—(1.) A furrow series of six or seven rather elongate 
spinelets, rather robust at the base, tapering and sharply pointed ; the median spinelet is 
the longest, and all radiate apart. (2.) On the surface of the plate is an obliquely trans- 
verse series of two or three robust conical spinelets, rather longer than any of the furrow 
series, the outer one being longest when two are present, and the middle one when there 
are three; on each side of these are two or three small spinelets near the margins of the 
plate. 
The mouth-plates are large, convex, and subtubercular ; and their surface is covered 
with short, conical, pointed spinelets, which decrease slightly in size as they recede from 
the mouth, but no definite order of disposition can be made out, and the mouth-plates 
have consequently a remarkably echinulate appearance. The true mouth-spines consist 
of a marginal series of about nine tapering, pointed spinelets on each plate, the two inner- 
most being fully twice as long and robust as the others, and slightly compressed. There 
are thus four powerful mouth-spines at each angle guarding the actinostome; and two or 
three of the superficial spines immediately behind these are equally robust. 
The actinal interradial areas are of very small dimensions, and the intermediate or 
ventral plates are few in number and do not extend beyond the fourth or fifth adam- 
bulacral plate. The separate plates are indistinguishable in spirit specimens, and their 
surface is covered with small, conical, and pointed spinelets. 
The anal aperture is central and distinct, often surrounded by larger spinelets. 
The madreporiform body is large, oval, and slightly convex, the inner end of the plate 
being about midway between the centre of the disk and the margin. Its surface is 
furrowed with numerous fine and deeply cut striations; many sharply bent and con- 
