492 THE VOYAGE OF H.M.S. CHALLENGER. 
conical spinelet, and on the surface of the plate a few small, equal, isolated, widely spaced, 
miliary spinelets. The basal plates are also similarly armed with a central conical spinelet 
and a few widely spaced miliary spinelets. The under-basals only bear miliary spinelets, 
and a few are present on the flanks of the dorso-central plate. 
The supero-marginal plates, about twenty in number from the median interradial line 
to the extremity, are large and narrowed abactinally (at least at the base of the ray), 
leaving small angular spaces in which the papular orifices are found. Each plate bears 
one large central spinelet and several smaller ones. The infero-marginal plates are much 
smaller than the supero-marginal series, diminish rapidly in size as they proceed along 
the ray, and do not reach the end of the ray, the adambulacral plates being there con- 
tingent on the supero-marginal series. Each plate, before they become very small, bears 
a large conical spinelet and two or three smaller ones. 
The adambulacral plates are small, rather broader than long, and with an angular 
prominence into the furrow; all the plates being equally prominent into the furrow. 
Their armature consists of a transverse series of three cylindrical tapering spinelets, nearly 
as large as the largest spinelet on the marginal plates. The innermost spinelet, which is 
rather smaller than the other two, stands at the apex of the angular prominence and is 
directed over the furrow, the other two are equidistantly spaced on the actinal surface of 
the plate and radiate slightly apart. The median spinelet is usually slightly the longest. 
About seven adambulacral plates are included within the wide actinal groove of the 
terminal plate. 
The mouth-plates trend upward towards the buccal cavity, and they bear on their 
surface two large robust actinal spines. The actinostome is large. 
I have found no trace of any actinal intermediate plates between the infero-marginal 
and the adambulacral plates. 
The madreporiform body is small and very difficult to see. It is situated between 
the basal plate and the innermost pair of supero-marginal plates, and is consequently quite 
at the edge of the disk. Its surface is traversed by what may be described as three or 
four very coarse ridges rather than striations, and it is essentially embryonic in character, 
The anal aperture, which is large and excentric in position, is situated between the 
dorso-central and basal plate, the margin of the former being deeply lunated for its 
reception. Several papilliform spinelets surround the orifice. 
The ambulacral tube-feet, which are arranged in two simple and regular rows, have 
fleshy terminal knob-like disks, which appear to be capable of invagination. 
The terminal plate is very large and deeply indented adcentrally for the reception of 
the termination of the median radial series of plates. It bears three large spinelets on 
each side near the extremity, and there appears to be a prominence in the median line 
abactinally on which a spine was probably originally borne. In addition to these, isolated 
miliary spinelets are also present on the surface. 
