140 BULLETIN OF THE 
shield are obscured by a thick skin, Under arm-plates somewhat obscured 
by skin, axe-shaped, with a broad curve without, a narrow angle within, and 
lateral sides slightly re-enteringly curved. Upper arm-plates long triangular, 
with an acute angle inward and a curve without. Side arm-plates large, 
meeting above and below, with a rounded, rather wide, but not very promi- 
nent spine-ridge. Disk regularly, but not very closely set with small, short, 
thick stumps (Fig. 276), each bearing a crown of blunt thorns, Radial shields 
and scaling hidden. Six cylindrical, opaque, blunt, slightly tapering arm- 
spines, which, under the microscope, are a little rough, but not thorny ; lengths 
to that of an under arm-plate 3, 2.2, 1.3, 1.2, 1.2, 1: 1. One minute pointed 
tentacle-scale. A young specimen from the same locality had a disk 4 mm. 
in diameter, and arms of 18 mm, The disk-stumps were closer set, and more 
like grains, and there were nine mouth-papille to each angle. 
This species is viviparous, It represents in the antarctic zone the arctic 
O. anomala, from which it differs in having a minute slender tentacle-scale and 
only five arms. 
Christmas Harbor, Kerguelen Islands, 120 fathoms, 1 specimen. Royal 
Sound, Kerguelen Islands, 25 fathoms, 1 specimen. Station 150, 150 fathoms, 
6 specimens, Station 151, 75 fathoms, 1 specimen, 
Ophiacantha sentosa sp. nov. 
Plate IX. Figs. 229 - 232. 
Special Marks. — Disk closely beset with short slender spines, with forked 
heads, encased in thick skin, so that they give the disk a furry look ; arm- 
spines slender and not thorny ; one minute rounded tentacle-scale. 
Description of an Individual (Station 298). — Diameter of disk 16 mm, 
Length of arm 80 mm. Width of arm without spines 3 mm, Mouth- 
papille nine or eleven, to each angle of which the innermost odd one is 
stoutest and spearhead-shaped, and is similar to and continuous with the 
teeth ; the outermost is very small and rounded, and the others are stout, 
conical, and pointed.  Mouth-shields small, wider than long; bounded 
within by an obtuse angle, and without by a curve. Side mouth-shields 
wider without than within, where they meet, of moderate width, and ex- 
tending well beyond mouth-shield on either side. Under arm-plates slightly 
swollen, much wider without, where they are gently curved, than within, where 
they present a peak, and are separated from the next plate ; lateral sides 
re-enteringly curved opposite tentacle-pores. Side arm-plates moderately 
prominent, meeting below, and beyond fourth joint, above also. Upper arm- 
‘plates about as long as broad, narrow fan-shaped, with an angle inward. Disk 
puffed, covered with a thick skin, which obscures the radial shields and seal 
ing, except a patch near mouth-shield ; the surface is closely set with small 
spines, about .8 mm. long, whose ends are forked, but which are more or less 
cased in skin. Seven regular tapering arm-spines, smooth, or bearing a few 
