228 MR. W. PERCY SLABElSr ON THE 



the space which intervenes between the marginal plates of either 

 side is covered with membrane. This band is nearly uniform in 

 breadth througbout, and is equal to one third of tlie greatest, 

 breadth of the ray ; it extends up to the extremity, the adoral 

 margin of the terminal plate being indented for its continuation. 

 The supero-margiaal plates are eight in number, counting from 

 the median interbrachial line and exclusive of the terminal. 

 Their shape is nearly quadrate, the most inward and the most 

 outward plates having the height rather greater than the length, 

 whilst those midway present the reverse proportions. The 

 infero-marginal series correspond in number with the superior 

 series and, excepting the innermost plate, have the length greater 

 than the height. Each of the supero-marginal plates normally 

 carries a minute tubercle or rudiment of an aborted spinelet ; 

 but in some instances even this is wanting. The terminal plate 

 is not at all gibbous or tubercular, and its size and outline is 

 conformable in every way to the regular tapering of the ray. 

 Three small delicate spines are borne on the terminal plate — 

 one placed at the extremity, in the median line, which points up- 

 ward and outward ; and one on either side, at a lower level, 

 which are separated by the furrow, and directed horizontally and 

 radiate slightly outward from the axial line of the ray. Cribri- 

 form organs three in each angle, the lateral ones very narrow, 

 all well spaced ; structure lamellif orm. 



Ambulacral furrows wide, straight or very slightly petaloid, 

 and open. Each adambulacral plate bears a single ambulacral 

 spinelet, also a rather large segmental pit and pajoilla. The 

 ambulacral spine, which is placed at the adoral extremity of the 

 plate, is comparatively robust, cylindrical, slightly tapering, and 

 longer than half the breadth of the furrow, over Avhicli it is 

 directed horizontally and slightly inwards (adorally). The 

 segmental papilla is subcircular in shape, nearly half as large as 

 the whole adambulacral plate, and is situated midway between 

 the bases of adjacent ambulacral sp)inelets, the margin towards 

 the furrow being straight. Towards the end of the ray the 

 papillae are turned back and directed slightly over the furrow, 

 instead of being closed down upon the surface of the plate; 

 and the pit is probably aborted. 



The mouth-plates form a rather broad mouth-angle, presenting 

 a well-developed keel along the median line of junction, more or 



