MONOGRAPH OF JAPANESE OPHIUROIDEA. 129 



times, and the lowest one about one and a half times, as long as 

 the corresponding arm joint. More distally, the arm spines become 

 rather rapidly fewer and shorter, so that in the tenth free arm 

 joint, they are five in number and about as long as the correspond- 

 ing arm joint. One tentacle scale, comparatively large, blunt in 

 the basal joints, but pointed more distally. 



Colour in alcohol white. 



I have observed the internal structures of this species, and 

 ascertained that the internal oral skeleton, genital plates and 

 generative glands are quite similar to those of the genotype 

 (Lyman, Challenger Kep., PL XLII, fig. 1). 



Ophiurothamnus, g- nov. 



Disk covered with rather coarse scales. Radial shields large 

 joined in pairs nearly along the entire length. Interbrachial 

 ventral surfaces small, with a pair of large, distinct plates joined 

 to each other in the interradial line. Another large, prominent 

 plate is present at the middle of the interradial margin, lying just 

 outside the paired plates mentioned. Genital bursse well developed. 

 Oral and adorai shields stout, the latter being entirely proximal 

 to the former. Three or four oral papillae on either side, the 

 outermost one being usually very large and wide. Teeth arranged 

 in a single vertical row. Dental papiUse absent. Arms strongly 

 knotted, with hour-glass -shaped joints. Dorsal arm plates very 

 small. Lateral arm plates well developed, those of the two sides 

 meeting above as weU as below. Ventral arm plates short, very 

 wide, as wide as the corresponding arm joint. Arm spines long, 

 slender, usually serrate ; those of the first one or two free arm 

 joints approximated dorsally. Lowest spine of the outer arm joints 

 hook-shaped. One tentacle scale to each pore. 



