REPORT ON THE ASTEROIDEA. 241 



the ray a longitudinal line which indicates the division of the superior and inferior series 

 of plates. At the actinal edge of the plates is a slightly longer, though still very short, 

 flattened and lancet-like spinelet ; and the series of these is likewise continuous throughout 

 the ray. In large examples, on the innermost ten or twelve plates, may be found a short' 

 flattened, squamule-like spine similar to those above described, placed on the middle of 

 the plate, both in the superior and inferior series, forming two exactly intermediate short 

 incipient series. 



The adambulacral plates are rather large and long, with a prominent angular margin 

 towards the furrow. Their armature consists of an inner or furrow series of five remark- 

 able spinelets enveloped in membrane. The median spinelet is the longest, and is directed 

 over the furrow at a right angle to the direction of the ray. It is compressed laterally, 

 more or less curved, often truncate at the extremity, and resembles a scimitar with 

 broad and flaring blade. The spinelet on each side is usually peculiarly curved, suggest- 

 ing the shape of a boomerang, and is flattened in the direction of the ray and has its 

 convexity turned towards the median spinelet. Often these spinelets appear clavate in 

 consequence of the fulness of the membranous sac in which they are encased. The outer 

 spinelet on each side is rather smaller than those just described, and has with its investing 

 membrane a distinctly papilliform character. On the actinal surface of the plate are 

 normally three longitudinal series of flattened squamiform papilla?, covered with mem- 

 branous sacs, all of uniform height, often somewhat irregular in position, and with three 

 to six in each series, the lines being often badly defined. These papillae are similar in 

 character to, and indistinguishable from, those on the actinal intermediate and infero- 

 marginal plates : indeed, when viewed superficially, it is usually impossible to say where 

 the one series ends and the other begins. 



The mouth-plates are elongate and very narrow, the united pair having a long fusi- 

 form outline. Their armature consists of a marginal series of sixteen to eighteen short, 

 cylindrical, obtusely-rounded papillae on each plate, increasing slightly in length as they 

 approach the anterior end ; the innermost two are larger than the rest, often more or less 

 curved ; and the innermost frequently has a boomerang form with its convexity directed 

 towards the corresponding spinelet of the companion plate, producing a character at once 

 conspicuous and remarkable. On the actinal surface of each plate is a single uniserial row 

 of low, broad, round-topped, transversely compressed, and closely crowded papilla?. About 

 sixteen or seventeen papilla? are in each series, and their breadth is nearly as great as that 

 of the plates ; the marginal series above noticed stand vertically and are appressed to the 

 side of the superficial series. All the papilla? are invested with membrane. 



The actinal interradial areas are narrow, but are occupied by numerous small imbricating 

 intermediate plates ; and these extend nearly to the extremity of the ray, in the form of 

 elongate narrow plates intermediate between the adambulacral and infero-marginal plates. 

 They bear skin-covered papillae precisely similar to those on the adambulacral and infero- 



(ZOOL. CHALL. EXP. — PART LI. — 1888.) 31 



