498 THE VOYAGE OF H.M.S. CHALLENGER. 
The supradorsal membrane is semitransparent, with closely and regularly reticulated 
fibrous bands, the bands (which are robust and massively coherent) forming definite meshes 
over the entire area. The disposition of the tendons is not in any definable relation to 
the spinelets. Hach mesh is filled up with a fine transparent tissue, in the centre of which 
is a single large spiraculum, surrounded by a conspicuous white ring. Consequent on 
the number and regularity of the meshes, the whole area is closely and uniformly covered 
with spiracula. 
The paxille are few in number and bear from three to five (or more) robust spinelets, 
which are well expanded and distributed pretty uniformly over the area, excepting the 
median interradial areas. ‘The rounded tips of the spinelets do not protrude, but simply 
elevate the supradorsal membrane into little rounded tubercles, which rise directly from 
the surface like warts, and, owing to their somewhat sparse distribution, impart a very 
characteristic appearance to the abactinal area of the starfish. Over the median portion of 
the rays and towards their extremities the tubercles are very much smaller in size and 
are more closely placed. A conspicuous subpentagonal ring of tubercles surrounds the 
centre of the disk at the base of the valves of the oscular orifice, the spinelets of fifteen 
paxillze contributing to its formation. The paxille stand at the base of each valve, one 
forming the actual support of the valve, and the other two being placed external to this, 
one on each side. Usually two of the spinelets of each of the outer pairs of paxille 
radiate outward and produce a very striking appearance on the abactinal area, as their 
whole outline and method of arrangement are perfectly discernible in consequence of the 
semitransparency of the membrane. The oscular orifice is of moderate size, the valves 
being subregular and closely reticulated. 
The ambulacral furrows, which are narrow, are more or less uniform in breadth except 
at the extremity, where they taper rapidly, and near the actinostome, where they are also 
constricted. The armature of the adambulacral plates consists of only one spinelet to each 
plate, which is comparatively long and cylindrical, and invested with membrane which 
develops a more or less extended sacculus at the extremity. The aperture-papillz are 
elongate, not tapering, nearly uniform in breadth, rounded at the extremity, almost as 
long as the spinelets on the adambulacral plates, and presenting a robust appearance in 
consequence of the investing membrane. 
The mouth-plates are comparatively small, short, and inconspicuous ; and the small 
secondary or superficial spine which stands on the median portion of each plate is 
moderately long and robust. The rest of the armature is indeterminable without damag- 
ing the specimen, in consequence of the extrusion of the stomach and other organs. 
The actino-lateral spines are regular and delicate, the twelfth from the mouth being 
longest. The spines preceding this one do not meet in the median interradial line, but 
are separated from those of the neighbouring ray by a uniformly narrow space, across which 
muscular fibres pass from side to side, uniting the tips of the corresponding spines on the 
