110 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



wide, with central area thick and elevated; surface more or less 

 tuberculous or rough. Interradial marginal plates of disk with 

 conspicuous tubercles; three or four similar plates distal to radial 

 shields at base of arm. First upper arm plate oblong, wider than 

 long; second and third triangular and somewhat swollen; succeeding 

 plates to tip of arm, minute, triangular. Interbrachial spaces below 

 covered by oral shield, genital scales and six or seven plates (in 

 each space), of which the marginal are greatly swollen; exact 

 arrangement of these plates variable; much smaller plates usually 

 scattered among them. Oral shields somewhat triangular, longer 

 than wide, very flat. Adoral plates large, wider without than 



within; oral plates small. 

 Oral papillae about five on a 

 side, outermost much the 

 largest; a pointed one at 

 apex of jaw. Genital slits 

 short, but genital scales 

 long and broad. First 

 under arm plate small, 

 somewhat hexagonal; sec- 

 ond and third more octag- 

 onal or even enneagonal, 

 second longer than wide, 

 third about as wide as long; 

 first and second and second 

 and third plates in contact; 

 succeeding plates small and 

 triangular, but persistent to 

 end of arm. Side arm 

 plates very large, somewhat 

 swollen, broadly in contact 

 above and below ; each plate 

 carries five or six short, 

 blunt, irregularly spaced arm 

 spines, scarcely one-third as long as joint. Tentacle pores small, 

 covered by a single scale, and confined to first and second joints of 

 arm. Color (dried from alcohol), yellow-brown, dull brownish, or 

 nearly white. 



Localities. — Albatross station 3661, off Uki Shima, Gulf of Tokyo, 

 Japan, 169 fathoms, mud, pebbles, 2 specimens; station 3704, off 

 Seno Umi, Japan, 94 to 150 fathoms, fine volcanic sand, 1 specimen; 

 station 4959, off eastern Japan, lat. 32° 36' 30'' N.; long. 132° 23' 

 20" E., 405 to 578 fathoms, green-brown mud, fine gray sand, for- 

 aminifera, 1 specimen; station 4965, off eastern Japan, lat. 33° 35' 

 20" N.; long. 135° 10' 50" E., 191 fathoms, dark green-gray sand, 



Fig. 40.— Ophiomusium trychnum. X3. a, prom above; 

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



DISK. 



