214 ME. W. PEECT SLADEN ON d?HE 



jjaxillse 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 either side. Usually two of the spinelets of each of 

 the outer pairs of paxillae radiate outwards and produce a very- 

 striking appearance on the dorsal 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 reticu- 

 lated. 



The ambulacral furrows are narrow and more or less uniform 

 in breadth, except at the extremity, where they taper rapidly, and 

 near the actiuostome, where they are also constricted. There is 

 only one ambulacral 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. Aperture- 

 papillse elongate, not tapering, nearly uniform in breadth, rounded 

 at the extremity, almost as long as the ambulacral spinelets, and 

 presenting a robust appearance in consequence of the investing 

 membrane. 



The mouth-plates are comparatively small, short, and incon- 

 spicuous ; and the small secondary surface-spine which stands on 

 the median portion of each plate is moderately long and robust. 

 The rest of the armature is indeterminable without damaging the 

 specimen, in consequence of the extrusion of the stomach and 

 other organs. 



Actino-lateral spines regular and delicate, the twelfth from the 

 mouth being longest. The spines preceding this one do not meet in 

 the median interbrachial line, but are separated from those of the 

 neighbouring ray by a uniform narrow space, across which mus- 

 cular fibres pass from side to side, uniting the tips of the corre- 

 sponding spines on either side. The tissue of the lateral web is 

 thickened along the margin, especially over the extremity of each 

 spine, to which it gives a rounded capitate appearance, the web 

 having the very faintest trace of incurving between the spinelets. 

 The thickening of the membrane just mentioned is much more 

 pronounced in the arm-angle, where all indentation of the web is 

 obliterated and indications are present of a tendency to excrescent 

 growth. A further faint line of thickening can be made out at 

 the union of the dorsal and ventral tissues, which occurs just 

 within the margin, especially round the shaft of the spines. 



Colour, in alcohol, greyish white. 



