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 ancular 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 papillee, 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 papille are similar in 
character to, and indistineuishable 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 papillz 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 papillz 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 papille 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 papillz precisely similar to those on the adambulacral and infero- 
(ZOOL. CHALL, EXP.—PART LI.—1888.) 31 
