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



above and below. Disk thick and puffed, rising well above the arms, with a con- 

 striction and furrow in each interbrachial space. The area between this constriction and 

 the radial shields, on either side, is occupied by four transverse plates running diagonally- 

 inward, and outside these is a similar larger plate forming the margin of the disk. 

 Central disk covered with fine overlapping scales, eight or ten on a line between central 

 point and inner angle of radial shield ; they are sparsely beset with minute stumps 

 bearing a crown of thorns. On the disk margin, over each arm, a few small grains or 

 stumps. Radial shields of a wide pearseed-shape, with an angle inward, nearly or quite 

 joined without ; separated within by a broad wedge of scales ; length to breadth, 

 2 '8 : 17. Near base of arm six strongly thorny, glassy, cylindrical, hollow arm spines, 

 whereof the two upper ones are very long, slender, and tapering, and the lowest is 

 thick and blunt; lengths to that of an arm joint, 5, 7, 3"5, 2-5, 2, 1'8 : I'S. Two large 

 pointed tentacle scales on the first pore ; one on each of those beyond ; toward middle of 

 arm the scales are more elongated and pointed, and have one or two microscopic thorns. 

 Colour in alcohol, very pale brown. 



Station 24. — March 25, 1873 ; off Culebra, West Indies; 390 fathoms; mud. 



Ophiomitra normani, Lym. (PI. XXVI. figs. 9-11). 



Opliiacantha normani, Lym., Bull. Mus. Comp. Zool., vol. vi., part 2, p. 58, pi. xv. figs. 414-416, 

 1879. 



Disk distinctly scaled and sparsely granulated, and with small, separated radial 

 shields. A single row of grains along the outer edge of the basal upper arm plates. 

 Four smooth, slender spines, the upper ones longest. 



(Type specimen from Station 232.) Diameter of disk 12"5 mm. Length of arm 

 about 40 mm. Width of arm next disk 2"5 mm. Seven widely spaced, cylindrical, 

 tapering, peg-like mouth papillae, three on each side, and one at apex of mouth angle. 

 Mouth shields a little broader than long, thick and square, with a little peak without 

 and within ; length to breadth, 1:2. Side mouth shields long and narrow, their outer 

 end wedged between the first and second under arm plates ; not quite meeting within. 

 First under arm plate well marked, of a rounded triangular shape, with the point 

 outward ; third plate, and those just beyond it, broader than long, bounded without by 

 a curve, on the sides by re-entering curves, and within by an angle ; length to breadth 

 (fourth plate), 1 "S : 1 7. Side arm plates with a swollen spine ridge, meeting below, but 

 separated above ; stout, and like the under plates, microscopically tuberculous. Upper 

 arm plates about as broad as long, short wedge shaped, with outer side curved and a 

 blunt angle within ; the first three or four have, along their outer margin, a single row 

 of rounded grains. Disk flat, somewhat angular, covered with well marked, pretty 

 equal, overlapping scales, whose surface is sparsely set with rounded grains, similar to 

 those of the upper arm plates ; interbrachial spaces below similarly covered, except that 



