226 MK. W. PEECr SLA.DEN ON THE' 



a similar incliDatioa also continued along the rays. The dorsal 

 surface of the rajs is consequently arched, and the supero-marginal 

 plates of the two sides almost meet in the median line, being 

 separated only by a narrow furrow. The actinal surface of the 

 ray is flat. The supero-marginal plates are higher than long, anil 

 each bears a large robust spinelet nearly as long as the height 

 of the plate. The innermost spinelet on each side of the arm- 

 augie is smaller than any of the others. There are seven supero- 

 marginal plates from the arm-angle to the tip of the ray, 

 exclusive of the terminal plate. This latter is large and very 

 prominent, compressed laterally, high, tubercular and rounded 

 dorsally, and bears four spines — one placed iu the median line 

 above the termination of the ambulacral furrow, and one on either 

 side of the furrow at a lower level, all the three being close 

 together at the very extremity ; whilst the fourth spine is placed 

 in the median line well back on the tubercular elevation of the 

 terminal plate. The infero-marginal plates, which are nine in 

 number, are longer than high and do not curve round on the 

 actinal surface, but rise abruptly at a sharp angle to it. At the 

 extremity of the ray there are occasionally two or three small 

 irregular supplementary plates intercalated between the dorsal 

 and ventral series, but which in no way interfere with the furni or 

 position of the terminal plate. Cribriform organs three in each 

 angle, well sejoarated, the median one broadest, each with a 

 depression down the median line; structure lamelliforni. 



Ambulacral furrows wide, straight and open. Adambulacral 

 plates elongate in the direction of the ray, their form simulating 

 the appearance in outline of caudal vertebrae. Each bears a 

 single short curved ambulacral spinelet articulated at the adoral 

 extiemity of the margin and usually directed transversely across 

 the furrow, or sometimes at an angle more adorally, the curvature 

 of the spine being downwards. Midway between the extremities 

 of the plate is placed a small, thin, semicircular scale-like papilla, 

 with the straight base upon which it is articulated running parallel 

 with the furrow, and having the rounded free lip directed out- 

 ward. Each of these papillae shut do.wn upon a small cavity or 

 pit, the function of which is as yet unknown. The cavities are 

 filled with very fine dark-coloured matter, which may either be 

 mud or excreted matter. I shall speak of these structures as 

 sefjmental pits and pa'pillae. 



