REPORT ON THE ASTEROIDEA. 619 
terminates. The membrane is furnished with elongate saccular bands placed saddle-like 
upon the truncately arched abactinal surface of the ray with great regularity, one on 
each side of each pair of ossicles, limited, however, to the sides, and not united across 
the median line. The sacculi extend from the horizontal line of the ambulacral ‘ verte- 
bree” to the margin of the ray, this dimension being about 2°5 mm., and the breadth of 
the band is about 0°75 tol mm. They have their surface crowded with very minute 
pedicellarize, visible only under high magnification. These are similar to those already 
mentioned, but are smaller, their length being about 0°11 mm, 
The section of the ray midway between the centre and the extremity gives an outline 
which may be described as subtriangular with the apex truncate, the greater portion of 
the base-line is occupied by the ambulacral furrow, the extremities of the line being 
represented by the adambulacral plates. 
The angular margin of the ray is fringed by a continuous series of elongate lateral spines ; 
these are attached to a rudimentary marginal plate ankylosed to the outer side of the 
adambulacral plates, and are directed horizontally and outward at an angle of less than 45° 
to the axis of the ray. They are usually borne on every other adambulacral plate, but 
occasionally they are present on two consecutive plates. Their presence is very irregular 
on the basal part of the ray (for about 25 mm.), and they are quite short and stunted (3°5 
mm. in length) until the ovarial region is passed ; they then increase in length, and con- 
tinue to increase gradually to a slight degree, their greatest length being near the middle 
of the ray, where they measure about 12 mm., and then after some distance gradually 
diminish in length towards the extremity. The spines are delicate and cylindrical, about 
0°26 to 0°3 mm. in thickness near the base, and taper throughout to an extremely fine, sharp 
poimt. The base forms a small condyle-like head, by which the spine is articulated to its 
plate. The spine is encased in a delicate membranous sheath, the surface of which is 
crowded with minute pedicellariz, so small as to be quite invisible to the naked eye, and 
only giving the appearance of a delicate superficial asperity on the spinelet when examined 
with a hand-magnifier. The sheath is prolonged for a short distance beyond the extremity 
of the spine in the form of a slightly bulbous sac, which is usually turned a little to one 
side as if the spinelet maintained an attachment to one of the lateral walls of the sacculus 
rather than occupying a central position; furthermore, the membranous sheath does not 
taper in conformity with the tapering of the contained spine (see fig. 4). The pedicellarize 
are of the same kind as those already noticed; they diminish a little in size as they 
approach the extremity of the spine, and the largest, which are situated near the base, 
measure about 0°1 to 0°116 of a millimetre in length. 
The ambulacral furrow occupies nearly the whole of the actinal surface of the ray, being 
2°5 mm. in width at a place where the whole ray is 5°75 mm. The adambulacral plates 
form the rest of the area, and have the appearance of constituting only a thin margin 
to the furrow; their shape as viewed from beneath is semicylindrical, with the furrow- 
