224 MR. W. PERCY SLADEN OK THE 



between the centre and the inner edge of the margiaal plates in 

 the arm-angle ; it tapers very slightly towards its extremity and 

 is indurated with spicular spitielets like the rest of the dorsal 

 membrane. 



The marginal plates form a deep margin and curve over 

 roundly in the interbrachial angles, the inferior as well as the 

 superior series being visible from above. Upon the rays the 

 superior series arch well over and almost meet in the median 

 dorsal line, giving to the ray a more or less subcarinate character. 

 The supero-margiual plates are four in number from the 

 median interbrachial line to the extremity, exclusive of the Inrge 

 terminal plate, and all are distinctly longer than high. The 

 second and third supero-marginal plates from the interbrachial 

 line bear short conical vipright spinelets ; but all the rest are un- 

 armed excepting the terminal plate, wliich carries three spines- 

 one at the extremity in the median line of the ray, and one on 

 either side at the anterior extremity of the inferior margin of the 

 plate. The terminal plate is swollen and prominently tubercular 

 dorsally, and is excavated on its outer extremity for the passage 

 of the terminal ambulacral tube. In one ray of the specimen 

 under notice, the penultimate supero-marginal plates are also 

 swollen and ankylosed, in such a manner as to resemble the 

 terminal plate, and bear a single spinelet. The infero-marginal 

 plates are iive in number, and are much shallower than the 

 superior series and also shorter. The two series consequently 

 do not correspond, a result probably brought about by the 

 extreme development of the terminal plate, which occupies the 

 space both of superior and inferior plate. Cribriform organs 

 one in each angle, rather broad and with a deep depression down 

 the median line ; structure lamelliform. 



Ambulacral furrows wide and open, occupying nearly the 

 whole of the actinal surface of the ray. Adambulacral plates 

 small, and form regular triangular prominences which indent, as 

 it were, the margins of the furrow. Ambulacral spines two on 

 each plate, short, subcorneal, sharply pointed or thorn-like, placed 

 side by side on the aboral side of the projecting angle; they 

 are consequently directed aborally and at an angle towards the 

 furrow, diverging also slightly from one another. 



Mouth-plates rather large, forming an acute angle adorally, 

 with an elevated angular ridge along the line of sutui^e, each 

 plate being strongly bent downwards and having the upturned 



