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, vmder 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-papillse to each angle. 



This species is Aiviparous. It represents in the antarctic zone the arctic 

 0. 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 rx. 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- 

 papilla) 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 scal- 

 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 



