20 G THE VOYAGE OF H.M.S. CHALLENGER 



7. Astropecten imbellis, Sladen (PL XXXIV. figs. 3 and 4 ; PI. XXXVIII. figs. 4-6). 

 Astropecten imbellis, Sladen, 1883, Joum. Linn. Soc. Lond. (Zool.), vol. xvii. p. 255. 



Pays five. P = 24 rum. ; r = 7 mm. R > 3*5 r. Breadth of a ray at the base, about 

 7 mm. 



Rays rather narrow, especially on the outer part, tapering continuously from the base 

 to the extremity. Interbrachial arcs subacute. 



The paxillar area has a comparatively open and irregular appearance, in consequence 

 of the character of the paxillae ; these have short thin pedicles, scarcely forming a true 

 tabulum, ;uid are surmounted by eight to ten rather long delicate spinelets, much longer 

 than the pedicle, which do not usually radiate apart widely. In consequence of the 

 rather wide separation of the paxillas, a somewhat "draggled" appearance is produced. 

 In the centre of the disk the paxillse are rather smaller and more crowded, and a central 

 eminence is present. 



The supero-marginal plates, which are eighteen in number from the median interradial 

 line to the extremity, are about as broad as high, but higher on the inner part of the ray. 

 The plates are slightly tumid, and form a well-rounded margin to the ray. The surface of 

 the plates is covered with very fine, closely placed, papilliform granules ; and the inner- 

 most eight or nine supero-marginal plates bear a small, delicate, sharply pointed spinelet, 

 about equal in length to the length of the plate, and placed near the middle of the 

 abactinal portion of the plate. The breadth of the plates is very little greater than the 

 length on the inner portion of the ray ; and on the outer portion these proportions are 

 reversed. 



The infero-marginal plates are broad, gently rounded towards the actinal surface, and 

 do not extend beyond the superior series. They bear three lateral spines, placed close 

 together in a very oblique series, the second from the margin being slightly the longest 

 and most robust ; all are exceedingly delicate, needle-like, and very faintly bent, the 

 longest being rather more than twice the length of the plate. On the innermost three 

 plates the upper or outer sjiine is the longest ; it is also flattened and much broader than 

 elsewhere. Excepting on the innermost three plates no other spines occur ; on these, 

 however, one or two very small ones are present in the median line. The surface of the 

 infero-marginal plates is covered with numerous minute papilliform squamules closely 

 placed, which become more spiniform towards the margins. 



Not more than two or three actinal intermediate plates are present, and these are 

 covered with short, papilliform spinelets similar to those just mentioned. 



The armature of the adambulacral plates consists of short, delicate, cylindrical spines, 

 slightly tapering at the tips, which form two series. The inner series consists of three 

 spines, the middle one slightly longest, radiating apart and directed over the furrow. The 

 outer series consists likewise of three similar and equal spinelets, usually directed towards 



