ASTEEOIDEA OP n.M.S. ' CHALLENGEE ' EXPEDITION. 219 



row or ridge of these spinelets stands on eitlier side of the 

 median line of a ray, forming a petaloid elevated area, which, 

 corresponds with the position of tlie underlying ray, and imparts 

 a very characteristic facies to the species. A prominent circle 

 surrounds the oscular orifice, marking out in a subpentagonal 

 outline the place of the attachment of the valve-spines. The 

 oscular valves are five in number, composed of rather short 

 radiating spines, forming regular triangular fans, the web which, 

 unites them being reticulated in a similar manner to the rest of 

 thie dorsal membrane. The valves, when closed, form a prominent 

 pyramidal peak in the centre of the disk. The reticulated dorsal 

 membrane reaches close up to the margin of the lateral fringe. 

 Ambulacral furrows distinctly petaloid. Ambulacral spines 



2, rather short, placed side by side well up in the furrow, and 

 forming a straight line parallel therewith. The spines of a pair 

 radiate slightly apart from one another in the plane of their 

 position ; and each is covered with, a tbick semitransparent mem- 

 brane, which is somewhat expanded, opposite the outer third of 

 the spine, imparting thereby an elongate subspatulate form, the 

 adoral spine of a pair being more robustly so than its companion. 

 Aperture-papillae small and short, suboval in form on the inner 

 portion of the ray, but becoming more elongate as they recede 

 from the mouth. 



Mouth-plates small, with strongly developed ridge at the line 

 of junction, and prominent peak aborally. Each plate bears two 

 short, robust, conical secondary surface-spines, one placed near 

 the adoral extremity, and the other about midway along the ridge ; 

 both spines are nearly equal in length, not longer than the ambu- 

 lacral spines, very wide at the base, and taper to a blunt extremity, 

 faintly bowed outward, and the tip approximated to the tip of 

 the corresponding spine on the companion plate. Mouth-spine.s 



3, small ; two situated at the extreme outer portion of the lateral 

 margin, one more inward. 



Actino-lateral spines about 24 on each side, 8th or 9th from 

 the mouth longest. The spines anterior to this are included 

 within the disk, their extremities reaching almost, but not quite, 

 up to the median interbracliial line. The succeeding spines 

 diminish in length gradually as they proceed outward, and even 

 towards the extremity remain comparatively long in comparison 

 ■with those of the other members of the genus. The actino-lateral 

 spines are very robust, and taper slightly to the tips, w^hich project 



