226 MR, W. PERCY SLADEN ON THE 



Valves 5, very regularly triangular, apices sharply pointed, all 

 webbed together, the whole forming a regular pyramid when 

 closed. The two innermost spines of each valve stand somewhat 

 apart, and the membrane is rather deeply drawn in between, pro- 

 ducing a well-defined furrow along the median line. The projecting 

 tips of spinelets are prominent at the sides of the valves. At the 

 base of each valve are two large elevated areas, formed by paxillse- 

 crowns of 6-8 spinelets, and thus nearly twice the size of the other 

 elevated tabulae upon the dorsal surface : they are subpentagonal 

 in shape; and the ten form a conspicuous and well-defined circlet 

 round the oscular pyramid. 



Ambulacral furrows rather wide, straight, uniform in breadth, 

 except at the extremity, where they rapidly converge. Ambu- 

 lacral spines 3, very short, cylindrical, slightly tapering, covered 

 with membrane, placed in line oblique to the furrow. Aperture- 

 papillae large and subcircular, with its investing membrane some- 

 what Japanese fan-shaped. The calcareous portion of the papilla 

 is very flaring in habit, sometimes appearing as if made up of a 

 comb of radiating spinelets. 



Mouth-plates small, short but broad, with widely-expanded 

 lateral flanges, broadly rounded in front, keel along line of junc- 

 tion feebly developed, aboral extremity only slightly prominent. 

 Two secondary surface-spines borne on slight tubercles, one near 

 the adoral extremity, and the other near the middle of the plate. 

 These spines are short, comparatively small, broad at base, and 

 taper slightly at the tip — the adoral pair being rather the smaller, 

 and not much larger than the ambulacral spines. Mouth-spines 

 3, similar in size and form to the ambulacral spines, arranged 

 on the lateral margin of the plate and away from the adoral peak 

 of the keel. 



Actino-lateral spines widely spaced, the difierence in the length 

 being comparatively small along the inner two thirds of the ray. 

 About 27 spines on each side of a ray, the 6th or 7th from the 

 mouth slightly longest. None of the spines meet in the inter- 

 brachial median line, but are widely separate; they are covered 

 with a thick fleshy tissue, which is slightly turned over the tips 

 of those spinelets that fall beyond the arm-angle, and is then ex- 

 tended in the form of a fleshy supplementary web or fringe, 

 which is very conspicuous in the arm-angle, and extends up to 

 within a short distance of the extremity of the ray, gradually 

 diminishing in breadth as it proceeds outwards. The margin of 



