REPORT ON THE ASTEROIDEA. 637 
it after a slight bulbous inflation. Further out on the ray the spines are very delicate, 
tapering, and sharply pointed, with the sheath more or less prolonged and a bulbous 
saccular expansion developed. At about the median third of the ray, the actinal spines on 
alternate plates are of different sizes, the plates which bear the lateral spine having a 
much shorter actinal spine than the others. Thus at 130 mm. from the disk the short 
spines are 6 mm. and the alternating long ones 10 mm. ; at 200 mm. from the disk (in 
another ray), the alternating spines are 3 mm. and 10 mm. respectively, and on another 
2°5 mm. and 9 mm. respectively at about the same distance. ‘The lateral spine is articu- 
lated on a prominent tubercle-like rudimentary infero-marginal plate ankylosed on the 
lateral surface of the adambulacral plate. It is remarkable for its great length and 
delicacy, the longest spines, which are situated at about 160 to 180 mm. from the disk, 
measuring 35 mm.; close to the ovarial region they are short, not more than 7 mm., 
but at 70 to 80 mm. from the disk they are 20 mm., and at 100 mm. from the 
disk 28 mm., and they increase as they proceed outward to the measure above indi- 
cated, and again diminish as they approach the extremity of the ray. The lateral 
spines, like the actinal spines, are encased in a very delicate, semitransparent mem- 
branous sheath, crowded with minute pedicellariz. These spines are extremely thin and 
delicate, and the invested shaft does not measure more than 0°216 mm. in thickness on 
the average. At the proximal extremity of the spines the membrane is seen to be con- 
tracted to the rim of the articulatory head of the spine, and is not continued as a uniformly 
broad sheath upon the tubercle ; at the distal extremity the sheath is slightly prolonged 
and a bulbous sacculus is developed. 
The actinostome occupies about half the actinal surface of the disk, its diameter being 
14°5 mm. in a disk measuring 28°5mm. The buccal membrane is thick and opaque. The 
mouth-plates are small and quite inconspicuous; the united pair have somewhat the form 
of a truncate wedge, the adoral margin being almost straight and with scarcely any pro- 
minence into the actinostome. The true mouth-spines are aborted, often absent altogether, 
but in some instances rudiments are present ; when this is the case the spinelets of the inner 
pair, which are very minute, are close together and enveloped in one common membranous 
sheath, the whole having the appearance of a little oviform scale pressed close against the 
mouth-plates; the outer pair, when present, are buried in the actinostomial membrane 
and appear to be merged in the ambulacral bar which crosses the furrow at the actino- 
stome ; their individuality is lost and usually no trace can be found of them. No pedi- 
cellarize are borne upon the rudimentary mouth-spines. Each mouth-plate bears one large 
robust secondary mouth-spine on its actinal surface, away from the adoral margin. There 
is thus a pair to each mouth-angle, and they are the only true spines present. The 
spines are 5 mm. in length, flattened at the tip, and slightly flaring, the flattened 
extremity being sometimes bifurcate. The shaft is encased in a delicate, semitransparent, 
