498 THE VOYAGE OF H.M.S. CHALLENGER. 



The supradorsal membrane is semitransparent, with closely and regularly reticulated 

 fibrous bauds, the bauds (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. Each 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 paxillse 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 tbe disk at the base of the valves of the oscular orifice, the spinelets of fifteen 

 paxillse contributing to its formation. The paxillse 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 paxillse 

 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 ambulacra! 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 spiuelet 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-papillae 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 



