NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 103 



swellings, which might perhaps be considered tooth papillae, but their 

 real nature is very doubtful. First under arm plate very small, pen- 

 tagonal, wider than long; succeeding plates pentagonal or squarish, 

 soon becoming roundish and more or less swollen, in contact with each 

 other outside disk. Side arm plates moderate, but concealed above 

 and, in part, on sides of arm, on basal half, by granules; each plate 

 carries two short, stout spines, low down, near under side of arm; 

 upper spine very short and thick, nearly spherical, about one-third 

 as long as joint; lower spine a trifle longer, not quite so stout, and 

 placed just proximal to tentacle, where it apparently functions as a 

 tentacle scale. Oral tentacle pore concealed by a single large scale of 

 very variable shape, sometimes nearly circular, more often truncate 

 and wide, like an outer oral papilla; between the two pores, in the 



a 



FIG. 38. OPHTOPENIA DISACANTHA. a, YOUNG, x"; b-d, ADULT, X5. a, PROM ABOVE; b, FROM ABOVE; 

 c , FROM BELOW; d, SIDE VIEW OF THREE ARM JOINTS NEAR DISK. 



midline of the arm, there projects a thick, plate-like outgrowth, which 

 is sometimes double and apparently acts as an inner scale for both 

 pores. Tentacle pores of arm without tentacle scales but protected 

 by lower arm spine. Color (dried from alcohol) , yellowish or very 

 light grayish. 



Localities. Albatross station 2849, off Alaska, lat. 55 16' N. ; long. 

 160 28' W., 69 fathoms, green mud, bottom temperature 43, 1 spec- 

 imen; station 2852, off Alaska, lat. 55 15' N.; long. 159 37' W., 58 

 fathoms, black sand, bottom temperature 41.8, 1 specimen; station 

 2854, off Alaska, lat. 56 55' N.; long. 153 4' W., 60 fathoms, black 

 sand, bottom temperature 42.8, 1 specimen; station 3227, Bering 

 Sea, lat. 54 36' 30" N.; long. 166 54' W., 225 fathoms, green mud, 

 bottom temperature, 38.6, 1 specimen; station 3312, Bering Sea, lat. 



