NORTH PACIFIC OPHIURANS IN NATIONAL MUSEUM CLARK. 199 



are usually much wider than long, but they are sometimes longer than 

 wide. None of the Albatross specimens have the under arm plates 

 as narrow as in Lyman's figures, and the upper arm plates are rela- 

 tively larger than he shows them, but I do not think these can be 

 specific differences. 



OPHIACANTHA ADIAPHORA, new species.o 



Disk 7 mm. in diameter; arms about 28 mm. long. Disk pentag- 

 onal covered closely with little stumps, nearly one-third millimeter 

 high, which are about 

 cylindrical and ter- 

 minate in several 

 slender, more or less 

 diverging teeth. Ra- 

 dial shields con- 

 cealed. Upper arm 

 plates small, nearly 

 triangular, widely 

 separated. Inter- 

 brachial spaces be- 

 low, like disk, except 

 that the scales are 

 visible just distal to 

 oral shield. Genital 

 slits small. Oral 

 shield rather small, 

 wider than long, 

 somewhat rhombic, 

 with rounded angles 

 and concave sides. 

 Adoral plates mod- 

 erate, wider without 

 than within, where 

 they do not always 



meet. Oral papillge FlG> W- OPHIACANTHA ADIAPHORA. x 7. a, FROM ABOVE; 6, FROM 



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



subequal, narrow, 



flat, bluntly pointed, three on a side and one at apex of j aw. First under 

 arm plate rather large, pentagonal, nearly as long as wide; succeeding 

 plates hexagonal, pentagonal, or tetragonal, much wider than long, 

 well separated from each other. Side arm plates rather large, meeting 

 broadly above and below, each with six or seven long, straight, 

 pointed spines; these spines are not perfectly smooth, but seem so 

 to the unaided eye; the uppermost (or one next to it) is the longest 



, signifying not different, in reference to the resemblance to 0. pentagona. 



