116 Mr. A. Alcock on 



sunk, by a deep groove passing across the base of every ray. 

 Eays long, semicylindrical, much constricted laterally at the 

 junction Avith the disk, and very deciduous. 



Abactinal surface of the disk with a reticulum of plates 

 embedded in tough membrane ; each plate bears a large spine 

 with its base sheathed in a globular fleshy mass closely 

 covered with minute pedicellarise ; the meshes between the 

 plates are perforated by jmpulge in groups ; numerous large 

 pedicellariffi fill the interbracliial arcs and extend nearly to 

 the actinostome. 



Abactinal surface of the rays with five beautifully regular 

 parallel rows of partly imbricating plates that may best be 

 described as compositely cruciform — that it to say, each com- 

 posite plate is made up of two cross series of tightly imbri- 

 cating platelets. The outermost row of plates on each side 

 forms a distinct supero-marginal series. All the plates are 

 embedded in a tough membrane, and each plate of the mid- 

 radial find supero-marginal rows, and in large specimens each 

 plate of the other two rows also, bears at the decussation of 

 its composite cross-pieces a large spine with its base en- 

 sheathed in a globular fleshy mass closely covered with 

 pedicellariaj ; other large pedicellari^ lie scattered over the 

 plates. The quadrangular meshes between the plates are 

 filled with papulae in oval plots of from five to nine. 



Marginal plates distinct ; the supero-raarginals, which 

 otherwise resemble the abactinal plates, are distinguished by 

 their mainly vertical direction, their long outer limbs forming 

 a high vertical palisade along tlie sides of the ray; the broad 

 intervals of the palisade are filled by papulee in groups. The 

 infero- marginals are simply oblong plates of small size lying 

 at right angles to the long vertical limb of the supero- 

 niarginals, and having a considerable lateral horizontal 

 bulge; each carries two strong horizontally-directed spines, 

 one above and behind the other, the upper being the larger 

 and exactly resembling the abactinal spines in form and in 

 its ensheathing fleshy pedicellaria-covered base, the lower 

 being quite simple. 



Adambulacral plates very small, but extending up into the 

 furrow ; each carries a pair of spines placed transversely, and 

 almost every alternate plate has inside the furrow a large 

 pedicellaria. 



The adambulacral plates are separated from the infero- 

 marginals by a single row of small narrow plates distant 

 almost their whole length apart, the long intervals between 

 the plates being filled each with a large papula encircled by 



