214 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



scattered spines are borne. Genital slits very lar^e. Oral shield 

 nearly trianp:iilar, rather wider than long. Adoral plates very large, 

 wider without than within where they meet. Oral papillae three on a 

 side and one at apex of jaw; the apical papilla and those on each side 

 are relatively huge, thick, rhombic, or triangular, and sharp; distal 

 papillae smaller, narrower, and blunter. First under arm plate 

 rather large, squarish, wider than long; succeeding plates separated, 

 somewhat pentagonal, with very wide distal margin, and narrow 

 proximal angle; toward the tip of the arm, the proximal half of 

 each under arm plate is very narrow. Side arm plates moderate, 



meeting slightly above 

 and below; each plate 

 carries six short arm 

 spines, of which the up- 

 permost is longest and 

 may equal three joints; 

 the upper ones are terete, 

 smooth, and pointed ; the 

 lower are flat and more or 

 less toothed or serrate on 

 the margins, as well as 

 rough on the surface; at 

 the base of the arm the 

 flattening is confined 

 chiefly to the lowest spine 

 of each series, but distally 

 all of the lower spines 

 show it to a greater or 

 less degree; of course, the 

 flatter the spine, the more 

 marked are the serrations. 

 Tentacle scale single 

 (rarely two on first pore of arm), rather large, flat, oval, pointed. 

 Color (dried from alcohol), light brown. 



Locality. — Albatross station 4928, off southern Japan, lat. 29° 51' N.; 

 long. 131° 2' 30" E., 1,008 fathoms, gray sand, globigerina, bottom 

 temperature 36.8°, 1 specimen. 



Type.— Cat. No. 25729, U.S.N.M., from station 4928. 

 This species is so well characterized by the disk covering, the huge 

 oral papillae, the big adoral plates and the serrate lower arm spines, 

 that it is not likely to be confused with any other. It would be 

 interesting to know whether it is strictly an abyssal form or, like 0. 

 hidentata, has a great bathymetric range. It is futile to speculate 

 on the basis of one specimen, but it is perhaps worth noting that the 



Fig. 99.— Ophiacantha prionota. x 5.5. a, from above; b, 

 FROM below; c, side view of two arm joints near disk. 



