REPORT ON THE OPHIUROIDEA. 177 



sides : they are highly arched, forming along the arm a longitudinal ridge. Side arm 

 plates small, with a rather low spine ridge, not meeting below or above. Upper arm 

 plates broader than long, slightly arched, four sided, broader without than within ; inner 

 and lateral sides straight, outer edge slightly curved. Disk flat, with interbrachial spaces 

 somewhat contracted, covered above and below by very minute, thin, overlapping scales ; 

 three to five in the length of a millimetre, and somewhat larger near margin. In each 

 brachial space there is a row of small rounded scattered plates radiating from the central 

 primary plate ; genital scales covered. Radial shields widely separated, long triangular, 

 and small, with an angle within ; length to breadth, 2:1. Four smooth, tapering, blunt, 

 nearly cylindrical arm spines, placed high on the sides of side arm plates near the outer 

 edge ; lengths to that of an arm joint, 1*8, 1"8, 1*8, 2 : 1*3. Two tentacle scales on each 

 pore, one large one on the interbrachial and a smaller one on the brachial side. Colour 

 in alcohol, pale brown ; upper disk inclining to olive. 



A smaller specimen with a disk of 13 mm. had arms 70 mm. long. It was similiar 

 to the adult, except that there usually were but three arm spines, and the second and third 

 mouth papillse from corner of mouth slit were flat and blunt. 



Station 232.— May 12, 1875; lat. 35°11'N., long. 139° 28' E.; 345 fathoms; sandymud. 

 Station 191.— September 23, 1874 ; lat. 5° 41' S., long. 134° 4' E. ; 800 fathoms; mud. 



Ophiochiton lentus, Lym. (PI. XXIII. figs. 16-18). 



Ophiochiton lentus, Lym., Bull. Mus. Comp. Zool., vol. vi. pt. 2, p. 55, pi. xiv. figs. 398-400, 1879. 



Three stout arm spines. Under arm plates thickened, but not forming a distinct 

 ridge. Scaling of disk smooth and uniform. 



(Type specimen from Station 171.) — Diameter of disk 13 mm. Width of arm close 

 to disk 2'5 mm. There are eleven short, sharp, stout, close-set mouth papdk-e on each 

 angle, the two outermost and the one at the apex being a little larger than the rest. 

 Mouth shields about as broad as long, of a rounded heart shape. Side mouth shields 

 extremely narrow, bent, wider without than within, where they meet. Under arm plates 

 large, swollen but not ridged, wider without than within, with lateral sides re-enteringly 

 curved, Side arm plates short and stout, with a low thick spine edge. Upper arm 

 plates twice as broad as long, of a fan shape, with inner arm truncated, or a diamond 

 shape with much rounded angles. Disk round, smooth and flat, covered with small, 

 pretty, uniform, rounded, overlapping scales, two or three in the length of 1 mm. Radial 

 shields small, twice as long as broad, with much rounded corners, separated their entire 

 length by two large round scales; length to breadth, 2:1. Interbrachial spaces below 

 covered with scaling similar to but finer than that above. Genital openings long, 

 extending from outer corners of mouth shield, where there are a few minute papilla?, to 

 margin of disk. Three stout, blunt, cylindrical, tapering, nearly equal arm spines, 

 about as long as an arm joint. Two round, flat, tentacle scales on the side arm plate, 



