114 OPHIUROIDEA. 
few papilliform spines on the most proximal upper arm-plate. 
Three arm-spines, the uppermost the longest ; the ventral plates are 
small, with a convex distal or, generally, a straight proximal edge. 
Arms seven to ten times diameter of disk. 
r= 5. 
Colour white or more mottled with darker. 
Distribution. North Atlantic (east side); Arctic Sea; ? off Marion 
Island. 50-2435 fms. 
a-n. 59° 26' N., 8° 23’ W., 705 fms. ‘Porcupine’ Exp. (St. 88). 
o-s. 60° 34' N., 4° 40’ W., 560 fms. ‘Porcupine’ Exp. (St. 77). 
t. 47° 38' N., 12° 8' W., 2435 fms. ‘Porcupine’ Exp. (St. 37). 
u,v. 47° 38' N., 12° 8' W., 400 fms. G. C. Bourne, Esq. 
Incertce sedis. 
3. OPHIOCHITON. 
Ophiochiton, Lyman, Bull. M. C. Z. vy. (1878) p. 182; ad. Chall. Rep. 
Oph. (1882) p. 176. 
Disk with fine imbricated scales. Radial shields small. Mouth- 
papille numerous; no tooth-papille ; teeth present. 
1. Ophiochiton ternispinis. 
Ophiochiton ternispinus, Lyman, Bull. M. C. Z. x. (1883) p. 255. 
Ophiochiton tenuispinus*, zd. t. ¢. pp. 228 & 285; Hoyle, Proc. Roy. 
Soc. Ed. xii. (1884) p. 709, § Proc. Roy. Phys. Soc. Ed, viti. 
(1885) p. 144. 
“ Special Marks. One tentacle-scale. Three slender, rather long 
arm-spines. 
“Description of an Individual. Diameter of disc 12 mm. Length 
of arm 60 mm. Width of arm near disc 2 mm, Twelve mouth- 
papilla to each angle, whereof the four inner ones, on either side, 
are short, pointed and spaced, while the two outer ones are flattened 
and crowded. ‘Teeth stout, flat, and shaped like a blunt spear-head. 
Mouth-shields regular pointed heart-shaped, with a small rounded 
lobe without. Length to breadth, 2: 1:3. Side mouth-shields very 
narrow within, where they barely meet; but spreading widely with- 
out, where they bound a part of the inner end of the genital opening. 
First under arm-plate rounded and small, not larger than the neigh- 
bouring mouth-papille. The plates beyond are much narrower 
than the arm; they are about as broad as long, much wider with- 
out than within, with an outer curve, reentering curves on the 
sides, and a truncated angle within. They are somewhat swollen, 
but have no ridge. Side arm-plates even, slightly flaring, nearly 
* As will be seen, the original namer of the species has, I suspect by a 
printer’s error, given two forms to his specific name. 
