ASTEEOIDEA OF H.M.9. ' CHALLENGER ' EXPEDITION. 241 



the membrane very slightly. The paxillae are clearly visible 

 through the transparent membrane ; and about nine longitudinal 

 rows may be counted across the base of the ray. The oscular 

 orifice is small, with the spines of the valves long and slightly 

 tapering. 



Ambulacral furrows narrow, lanceolate, maintaining a nearly 

 uniform breadth till near the extremity. Ambulacral spines 3 to 

 5 in number, rather long, delicate and acicular, arranged on the 

 adambulacral plate in a semicircular curve when the larger num- 

 ber are present — three usually being on the margin o£ the furrow, 

 and the two adoral ones standing successively more outward 

 (away from the furrow) on the plate. These two obliquely placed 

 spinelets maintain their position throughout the ray ; and any 

 diminution which takes place in the number towards the extre- 

 mity is manifest in the marginal or aborally placed members of 

 the series. The most aboral spine is rather shorter than the 

 others, which are nearly uniform in length ; and each of them is 

 invested with a very thin membrane, and no sacculus is produced. 

 The first adambulacral plates (nearest the mouth) bear only two 

 spines ; and these sometimes are webbed together. 



The aperture-papillse are small and dumpy, the calcareous por- 

 tion being little more than twice (or at most three times) as long 

 as broad ; and very frequently this is bulged out somewhat at the 

 side. The papilla is not free as usual in this genus, but is 

 clothed with the general tissue of the actiual area, the aboral 

 lateral margin alone being free and forming the actual lip of the 

 segmental aperture as in Pteraster ; the papilla fits close up to 

 the spine, aboral to it, and slants rather obliquely in consequence. 



The mouth-plates are small, short, narrow, both plates elevated 

 prominently rather than forming a true keel at the j unction ; 

 aboral extremity gently rounded, not prominent. Each plate bears 

 two large, robust, conical secondary superficial spinelets, longer 

 than the plates themselves, tapering to a fine point, and their bases 

 occupying nearly the whole of the length of the short plate. 

 These spines stand perpendicular to the superficies, the aboral 

 pair radiating rather wider apart and more outward than the 

 adoral pair. Mouth-spines 2 (or 3 ?), delicate, pointed, rather 

 wide apart, and placed on the lateral margin of the plates opening 

 into the peristomial circle. 



Actino-lateral spines comparatively robust and well spaced, 

 16 to 17 on each side of a ray, the fifth from the mouth being 



