2S2 MB. W. PEBCY SLADEN ON THE 



form a more or less distinctly visible Maltese cross, in consequence 

 of two prominent fibres joining the tips of the opposite spinelets. 

 Oscular orifice moderately large ; circumference at the base of 

 the valves very clearly marked out by prominent spinelets. Valves 

 triangular, 5 in number, forming a regular pyramid ; the whole 

 series webbed together with a membrane clo sely punctured with 

 spiracula like the rest of the dorsal area, and with 2 or 3 promi- 

 nent spinelets projecting along the sides of each valve. 



Ambulacral furrows rather wide, subpetaloid, or gracefully 

 lanceolate. Ambulacral spines 3, short, delicate, slightly tapering, 

 nearly equal in length, covered thinly with membrane, but with 

 no saccular extension present. Each series placed slightly ob- 

 lique to the median line of the ray. Aperture-papillae large and 

 squarely oval, with a thick plump sacculus, and attached close up 

 to the outer extremity of the diagonal series of ambulacral 

 spinelets. 



Mouth-plates very elongate and remarkably narrow, the pair 

 together forming a prominent, elevated, rounded ridge, tapering 

 and roundly pointed at either extremity. Near the adoral extre- 

 mity of each plate stands a single, rather large spine, subconical. 

 becoming attenuated towards the extremity, but not pointed. 

 These spines are directed horizontally over the peristome, the pair 

 in each mouth-angle diverging slightly apart from one another 

 and away from the median line of the mouth-plates ; these are 

 the anterior pair of secondary mouth-spines, placed unusually 

 forward. Prom the superficies of each mouth-plate, and about one 

 third from the inner or adoral extremity, rises a second, robust, 

 subconical, and moderately long spinelet, directed downwards and 

 slightly inwards. Both these pairs of secondary superficial spine- 

 lets are about equal in length to the ambulacral spinelets, but are 

 more robust, the aboral being stouter but rather shorter than 

 the companion pair. Mouth-spines 4 or 5, short, subcylindrical, 

 thickened at their bases, placed on the margin of the plates, and 

 directed horizontally. These spines are much smaller and shorter 

 than the secondary superficial spines above noted, and are attached 

 to a wide lateral extension or flange of the mouth-plate. 



Actino-lateral spines long and rather widely spaced, the longest 

 about midway out on the ray (the eleventh from the mouth) ; 

 about 40 in all. The spines within the disk come nearly up to 

 the median interradial line, but do not meet. The spines whose 

 free extremities fall in the marginal fringe diminish gradually 



