MONOGRAPH OF JAPANESE OPHIUROIDEA. 143 



inner sides, onter side convex as a whole, bnt sliglitly concave at 

 the middle, wide and very short. Successive plates separated from 

 one another; distally they become rapidly smaller, and the outer 

 border is then entire. Arm spines conical, acute, short, shorter 

 than the corresponding arm joint ; upper ones longer, lower ones 

 somewhat rough at the end, looking like compound hooks towards 

 the extremity of the arms. They are about seven in number in 

 the first basal joints, but rapidly decrease in number as w^ell as 

 in size, so that, on the eighth lateral plate, they are only four 

 and about half as long as the corresponding joint. 



The plates of the disk and arms are shagreened. 



Colour in alchohol : disk gray, arms banded with grayish 

 brown and white. 



The present species is very closely related to 0. ohslricta 

 (Lyman), but differs from it chiefly in the presence of the prom- 

 inent tubercles on the disk and in the radial shields joining in 

 pairs in the radial line. In the first mentioned character, this 

 species closely resembles OpJiiogj/ptis nodosa Kœhlee, 1905. 



Order iii. gnathophiurida Matsibioto. 



Disk covered with fine, imbricating scales, which are very 

 regular in size and arrangement. Radial shields well developed, 

 each having a conspicuous articular pit near the outer end for the 

 reception of a large, ball-like articular condyle of the genital plate. 

 Genital plates usually fixed to the basal vertebrœ. Genital scales 

 short, wide, flat, leaf -like, articulating with the genital plates near 

 the outer end of the latter. Besides, an additional scale is present 

 on the abradial border of the innermost part of each genital slit, 

 being also short, wide, flat, loaf- like and firmly fixed to the oral 



