420 THE VOYAGE OF H.M.S. CHALLENGER. 
to the extremity of the delicate innermost spine. One or two small ciliary spines may 
be present on the extreme outer edge of the adambulacral plate, adjacent to the first 
longitudinal row of intermediate plates ; and two or three similar small spines are present 
in the same position at the outer edge of the non-prominent intermediate adambulacral 
plates, but no spines whatever are present on the surface of these plates within the 
furrow. 
The actinostome is deeply depressed, and the mouth-plates are entirely within the 
cavity, and are not apposable. Their armature consists of pointed, moderately robust 
spines similar to the larger spines on the ridges of the adambulacral plates. 
The madreporiform body, which is small and inconspicuous, is placed external to one 
of the interradial (basal) plates. 
The anal aperture is small, distinct, surrounded by a circlet of small ciliary spines, 
and is placed at the side of the dorso-central plate, and consequently slightly excentric 
in position. 
The ambulacral tube-feet form four rows. They are rather small, subconical, and 
have a small but distinct fleshy terminal disk. 
Young Phase.—The young form,’ measuring R=11 mm., r=2'25 mm., has a very 
remarkable appearance, owing to the prominence and distinctness of the component parts 
of the skeleton. The disk is much higher than in the adult. The dorso-central plate is 
prominent and assumes the shape of a rounded cone. The basal or interradial and first 
radial plates are of nearly equal size, and are very tumid or almost semiglobular in form. 
The plates of the median radial line are large and distinct, occupying a large portion of 
the abactinal surface of the ray. The supero-marginal series of plates form the margin of 
the ray and the intermediate plates are small. Between the supero-marginal series and 
the adambulacral plates there are not more than two fully developed longitudinal rows of 
plates, with a partially developed series commencing to appear between the latter and the 
adambulacral plates. ‘The terminal (ocular) plates are very large, somewhat resembling 
the shape of a serpent’s head, and are armed with one or two pairs of comparatively large 
robust spinelets, near the extremity, which are directed upward. 
The large plates of the disk and the median radial series have already a small tubercle, 
but only some of these bear spinelets. All the plates have a few widely spaced and very 
minute granules and microscopic ciliary spinelets. The spinelets on the lower rows of 
plates are comparatively long and well developed. ‘The character of the alternate pro- 
minent adambulacral plates is already discernible, although not more than one or two 
spinelets are present in the armature of each. 
The madreporiform body is outside and external to the interradial or basal plate, and 
almost in the ravine of the interbrachial arc. The anal aperture is excentric, and 
1 T have given a drawing of this young example in my account of the Asteroidea dredged during the cruise 
of H.M.S. “Triton” (Zrans. Roy. Soc. Edin., 1883, vol. xxxii. pl. xxvi. figs, 9-11). 
