240 MB. W. PEKCT SLADBTSr ON THE 



dorsal and the ventral areas respectively. "When viewed from 

 above they are seen to encroach on the dorsal area to a very 

 slight degree, and still less on the ventral. Along the free por- 

 tion of the ray the supero-marginal plates of the two sides of 

 the ray meet in the median dorsal line and entirely encase the 

 ray ; in consequence of the regular rounding of the plates, the 

 ray assumes a perfectly cylindro-conical form, tapering to the tip, 

 and suggesting the appearance of a delicate belemnite. 



The supero-marginal plates are 43 or 44 in number, counting 

 from the tip of one ray to the tip of the neighbouring ray, exclu- 

 sive of the terminal odd plates, the odd number arising from a 

 marginal plate being placed in the median iutei'brachial line, 

 instead of a sutural division as usual in Porcellanaster. All the 

 marginal plates are devoid of spines or tubercles ; and in both 

 the superior and inferior series the height is greater than the 

 length, throughout the ray. The infero-marginal plates correspond 

 exactly with the superior series, and their height may also be 

 said to be equal. A few very small conical granules, evidently 

 loosely attached, are present on the surface of the marginal 

 plates, especially on those which border the disk, and chiefly 

 grouped near the ventral margin of the infero-marginal plates 

 and the dorsal of the superior series. The terminal plate is very 

 small and inconspicuous, in no way gibbous or exceeding the 

 natural conformity as ti]D of the tapering ray, and is entirely 

 devoid of spines. Seen in lateral profile, the tip of the ray shows 

 a very faint tendency to an upward curve, produced by the slightly 

 elevated position of the terminal plate and the curving upward 

 of the ventral area. Cribriform organs 14 in each angle, very 

 narrow ; structure papilliforin. 



The ambulacral furrows are narrow, and when in a state of 

 contraction entirely conceal the sucker-feet. The adambulacral 

 plates are longer than broad, but are quite inconspicuous, their 

 form and even the divisional sutures being masked by the mem- 

 brane and spinelets with which they are covered. Along the 

 furrow-margin of the plate are 5 ambulacral spines, and the series 

 of these form a continuous straight line throughout the ray, with- 

 out curve or break of any kind. These spines are short, robust, 

 truncate at the extremity, and flat, their breadth being placed 

 at right angles to the furrow, and all are equidistantly spaced 

 apart. Behind the furrow-series each adambulacral plate bears 



