516 THE VOYAGE OF H.M.S. CHALLENGER. 



a regular pyramid ; the whole series are webbed together with a membrane closely punc- 

 tured with spiracula like the rest of the supradorsal membrane, and there are two or three 

 prominent spinelets projecting along the sides of each valve. 



The ambulacral furrows are rather wide, subpetaloid, or gracefully lauceolate. The 

 armature of the adambulacral plates consists of three short, delicate, slightly tapering 

 spines, nearly equal in length, and covered thinly with membrane, but with no saccular 

 extension present. Each series is placed slightly oblique to the median line of the ray. 

 The aperture-papillae are large and squarely oval, with a thick plump sacculus, and are 

 attached close up to the outer extremity of the diagonal series of spinelets on the adam- 

 bulacral plates. 



The mouth-plates are very elongate and remarkably narrow, the pair together forming 

 a prominent, elevated rounded ridge, which is tapering and roundly pointed at each ex- 

 tremity. Near the adoral extremity of each plate stands a single, rather large spine, 

 subcorneal, and becoming attenuated towards the extremity, but not pointed. These 

 spines are directed horizontally over the peristome, the pair in each mouth-angle diverg- 

 ing slightly apart from one another and away from the median line of the mouth-plates ; 

 these are the anterior pair of secondary mouth-spines, placed unusually forward. From 

 the superficies of each mouth-plate, and about one-third from the inner or adoral extremity, 

 rises a second, robust, subconical, and moderately long spinelet, directed downward and 

 slightly inward. Both these pairs of secondary or superficial spinelets are about equal in 

 length to the spinelets on the adambulacral plates, but are more robust, the aboral being 

 stouter but rather shorter than the companion pair. The mouth-spines, which are four or 

 five in number, are short, subcylindrical, thickened at their bases, placed on the margin of 

 the plates, and directed horizontally. These spines are much smaller and shorter than 

 the secondary or superficial spines above noted, and are attached to a wide lateral exten- 

 sion or flange of the mouth-plate. 



The actino-lateral spines are long and rather widely spaced, the longest being about 

 midway out on the ray (the eleventh from the mouth) ; about forty in all are present, The 

 spines within the disk come nearly up to the median interradial line, but do not meet. 

 The spines whose free extremities fall in the marginal fringe diminish gradually and with 

 regularity up to the extremity, the last few maintaining, however, a nearly uniform 

 length, which gives a rounded appearance to the fringe at the ray-tips. The actino- 

 lateral spines are finely pointed at their extremities, and the web-membrane is moderately 

 indented between them ; the marginal fringe is perfectly even and regular, forming a 

 conspicuous marginal border when seen from the upper surface, although the reticulated 

 supradorsal membrane is continued close up to the margin. 



Colour in alcohol, greyish white. 



Locality. — Station 300. Off the coast of South America, between the Island of Juan 

 Fernandez and Valparaiso. December 17, 1875. Lat. 33° 42' 0" S., long. 78° 18' 0" W. 



