MONOGRAPH OF JAPANESE OPHIUBOIDEA. 105 



ventral arm plate small, pentagonal, with wide and truncated inner 

 angle and curved outer side, wider than long. The rest are 

 large, pentagonal, with wide inner angle and perfectly rounded outer 

 angles, much wider than long. Arm spines long, slender, hyaline, 

 flattened and thorny, except the uppermost one or two which are 

 nearly terete ; upper ones longer ; the uppermost spine is about 

 two to three times, and the lowest one about two-thirds, as long 

 as the corresponding arm joint. From the seventh or eighth joint 

 outwards the lowest spine is transformed into a compound hook, 

 being shghtly bent inwards and bearing series of booklets on the 

 inner side. The arm spines are seven or eight in number and 

 approximated dorsally in the basal joints, but rapidly decrease in 

 number outwards, so that they are four or five in the tenth 

 joint. One tentacle scale, small, oval and flat. 



Colour in alcohol white. 



In one of the specimens, the tubercles of the disk are fewer, 

 but in the second, they are larger, and the stelliform crowns are 

 more complex, some of the rays bearing two or three denticles 

 each. In the third specimen, the disk scales are coarser than in 

 the other two, and the radial shields are slightly longer than 

 wide. 



Tliis new species is near to OpJdomitrella partita (Lütken & 

 MoKTENSEN, 1899), but differs from it chiefly in the smaller radial 

 shields, in the disk tubercles having more slender stem and larger 

 crown, in the arm spines being approximated dorsally in the first 

 basal joints, and in the lowest arm spine being transformed into 

 a compound hook. The six rays of the crown of the disk tubercles 

 are formed by the bifurcation of the three primary rays, so that 

 the disk tubercles are fundamentally of the same plan in both 

 species. 



