REPORT ON THE OPHIUROIDEA. 191 



spines, of which, however, the upper one is much the stoutest ; lengths to that of an arm- 

 joint, 1-8, 1-6, 1-5, 1-5, 1-5 : T2, or 2% 1*6, 1"5, 1'3, 1-3, 1'3 : 1*2. Tentacle scales flat, 

 pointed, and rather small. Colour in alcohol, pale brown. 



The species stands near the typical Ophiacantha setosa in respect to form of disk and 

 length of arm ; but it differs from this and most others of the genus in having naked 

 radial shields and side arm plates which do not project to give a knotted look to the 

 arm. 



Station 33. — April 4, 1873 ; off Bermudas ; 435 fathoms ; mud. Two specimens from 

 the " Blake " expedition, dredged in 101 fathoms by A. Agassiz, showed no important 

 variations. The disk-grains were larger and more numerous. 



Ophiacantha cuspidata, Lym. (PI. XV. figs. 9, 10 ; PL XLI. figs. 12-14). 



Ophiacantha cuqritlofa, Lym., Bull. Mus. Comp. Zool., vol. v., part 7, p. 143, pi. x. figs. 

 248-250, 1878. 



Disk beset with thorny stumps ; eight rather long, stout, and feebly thorny arm 

 spines ; about eleven long slender mouth papillae. 



(Type specimen from Station 344.) Diameter of disk 9 mm. Length of arm 63 mm. 

 Width of arm without spines 3 mm. Ten or sometimes eleven long, flat, rather slender 

 and irregular mouth papillae, of which the outer one has often a spatula shaj^e. Teeth 

 long, spearhead-shaped. Mouth shields small, long pentagonal, with a wide obtuse 

 angle within ; length to breadth, 1:1. Side mouth shields small, narrow and crowded, 

 meeting within. Under arm plates wider without than within, where they touch the 

 next plate ; bounded without by a rounded angle or a somewhat deep curve, within by 

 a more gentle curve, and on the lateral sides, opposite tentacle scales, by re-entering 

 curves. The second plate is narrower within, and has a wavy outer edge. Upper arm- 

 plates fan shaped, with an angle inwards ; the lateral corners are sharp, and the lateral 

 sides slightly re-enteringly curved. Side arm plates moderately prominent, meeting 

 narrowly above, but not below at base of arm. Disk moderately thick, not puffed, closely 

 set with stout little stumps, each bearing a crown of five or six minute thorns. Radial 

 shields and disk scales hidden by skin and the thorny stumps, except that the position 

 of each radial shield is usually marked by a shallow furrow. Eight stout, lon°-, 

 cylindrical arm spines, tapering to a blunt point and set with fine thorns ; lengths to 

 that of an arm joint, 3-6, 5, 3, 2, 2, 2, 1*8, 1-4:1. On first pore two tentacle scales; 

 on the rest a single large pointed scale. Colour in alcohol, dark straw. 



A young specimen with a disk of only 1'5 mm. had an arm of 10 mm. The disk 

 armature consisted of little crochets with two or three prongs ; the arm joints were of course 

 more constricted, and the upper jmd under arm plates were widely separated ; there 

 were four or five arm spines, whereof the first or second was much the longest ; to each 



