l96 THE VOYAGE OF H.M.S. CHALLENGER. 



Ophiacantha discoidea, Lym. (PI. XXVI. ligs. 1-3). 



Opliiacantlia discoidea, Bull. Mus. Comp. ZooL, vol. vi., iwrt 2, p. 57, pi. xy. figs. 405-407, 

 1879. 



Seven or eight slender, translucent, nearly smooth arm spines. A small spine-like 

 tentacle scale. Disk densely set with minute stumps crowned with thorns. 



(Type specimen from Station 190.) Diameter of disk, 47 mm. Arms broken ; they 

 were ]3lainly long, because, in their first 15 mm. there was scarcely any tapering. Width 

 of arm near disk 1 mm. Three cylindrical, blunt, peg-like mouth papillas on each side, 

 and a similar but longer one at apex of mouth angle. Teeth longer than wide, with a 

 rounded cutting edge. Mouth shields broader than long, regular heart-shaped, with 

 point inwards; length to breadth, 7:1. Side mouth shields very wide without, and 

 overlapping the first under arm plate, but tapering to a thin point within, where they 

 scarcely meet. First under arm plate longer than broad, and somewhat overlapped by 

 side mouth shields ; the plates just beyond are much wider than long, of a wide axe- 

 shape, with a broad curve without, short re-entering curves on the sides, and an obtuse 

 angle within. Side arm plates meeting above and l^elow, stout and flaring, with a strong 

 spine crest. Upper arm plates fan-shaped, with the angle inward ; widely separated. 

 Disk nearly round, a little pufied, closely and evenly set, except in the middle, with very 

 short microscopic stumps crowned with three or four little thorns. No scales or radial 

 shields appear in the alcoholic specimen. Seven or eight slender, pointed, translucent, 

 nearly smooth arm spines, whereof the two uppermost are nearly as long as two joints; 

 while those below gradually diminish in length to the lowest, which is two-thirds as long 

 as a joint. One narrow, pointed tentacle scale. Colour in alcohol, pale brownish-grey. 



Station 190.— September 12, 1874; lat. 8° 56' S., long. 136° 5' E. ; 49 fathoms; 

 mud. 



This species stands nearest, perhaps, to Ophiacantha cosmica from which it is distin- 

 guished by different under arm plates, smaller side mouth shields, stouter disk stumps, 

 and a very narrow spine-like tentacle scale. 



Ophiacantha levispina, Lym. (PI. XXV. figs 1-3). 



Ophiacantha levispina, Lym., Bull, Mus. Comp. Zool., vol. v., part 7, p. 147, pi. x. fig. 277, 

 1878. 



Disk closely beset with fine stumps bearing crowns of minute thorns ; seven slender, 

 not thorny arm spines ; outer side of under arm plates strongly curved. 



(Type specimen from Station 214.) Diameter of disk 6 mm. Length of arm 36 mm. 

 Width of arm without spines 2 mm. Mouth papillae seven to nine to each angle, whereof 

 the outer one on either side is broad and scale-like, while the other five or seven are sharp 

 and conical. Mouth shields broad heart shape, with the point inward ; length to breadth, 



