86 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



large, somewhat triangular, nearly twice as long as wide, well sepa- 

 rated within but touching distally. Upper arm plates tetragonal 

 (becoming triangular on distal half of arm), with distal margin con- 

 vex and much longer than proximal; lateral margins somewhat 

 concave, and distinctly longer than distal; only first six or eight, 

 in contact. Interbrachial spaces below covered by fifteen to twent} r 

 irregular plates. Genital slits long and conspicuous, bounded by 

 very large genital scales; each scale carries near its distal end a few 

 blunt papillae, which are flat, squarish, and closely in contact with 

 each other, when seen, as an arm comb, from above. Oral shields 

 large, about as long as broad, or longer, somewhat pentagonal. 

 Adoral plates long and narrow, meeting within; oral plates rather 

 large, three times as long as wide. Oral papilla? about five on a side, 

 subequal, squarish but pointed, crowded. First under arm plate 

 large, hexagonal, much wider than long; succeeding plates triangular 



FIG. 27. OPHIUBA ATACTA. X8. O, FROM ABOVE; b, FROM BELOW; C, SIDE VIEW OF TWO ARM JOINTS 



NEAR DISK. 



or pentagonal, wider than long, only first two, or none, in contact. 

 Side arm plates large, broadly in contact below and above, except 

 at very base of arm; each plate carries three short, subequal, bluntly 

 pointed arm spines, about half as long as joint. Oral tentacle pores 

 open into mouth slit ; each pore with five or six scales on either side ; 

 next two or three pores with three or two scales on side arm plate, 

 proximally; remaining pores with a single small scale. Color (dried 

 from alcohol), nearly white. 



Locality. Albatross station 3338, off Aleutian Islands, lat. 54 

 19' N., long. ; 159 40' W., 625 fathoms, green mud, sand, bottom tem- 

 perature 37.3, 1 specimen. 



Type. Cat. No. 25533, U.S.N.M., from station 3338. 



In several particulars this specimen resembles monostcecha, but it 

 can not be referred to that species, the radial shields and upper arm 

 plates are so different, aside from other minor points. The peculiarly 



