REPORT ON THE OPHIUROIDEA. 187 



diamond-shape. Side mouth shields short, wide, slightly curved, not meeting within. 

 They and the mouth 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 prominent spine ridge. Disk 

 regularly, but not very closely set with small, short, thick stumps, each bearing a crown 

 of blunt thorns. Eadial 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, r2, 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 papillae to each angle. 



This species is viviparous. It represents in the antarctic zone the arctic Ophiacantha 

 anomala, from which it differs in having a minute slender tentacle scale and only five 

 arms. 



Christmas Harbour, Kerguelen Islands ; 120 fathoms. Royal Sound, Kerguelen 

 Islands ; 25 fathoms. Station 150.— February 2, 1874 ; lat. 52° 4' S., long. 71° 22' E. ; 

 150 fathoms ; rock. Station 151. — February 7, 1874; off Heard Islands; 75 fathoms; 

 mud. Kerguelen Islands ; 120 fathoms. 



Ophiacantha sentosa, Lym. (PI. XIII. figs. 10-12). 



Ophiacantha sentosa, Lym., EuU. Miis. Comp. Zool., vol. v., part 7, p. 140, pi. ix. figs. 229-232, 

 1878. 



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. 



(Type specimen from Station 298.) Diameter of disk 16 mm. Length of arm 80 mm. 

 Width of arm without spines 3 mm. Mouth papillae 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 extending 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-enteriugly 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. 



