MONOGliArH OF JAPANESE OrHIUROJDEA. 135 



extent. First ventral arm plate comparatively large, hexagonal, 

 with concave inner side and convex surface, widest at the lateral 

 angles, as long as or slightly longer than wide, in contact with 

 the next plate, which is the largest of all, pentagonal, widest at 

 the lateral angles, as long as or slightly longer than wide, and 

 has ■ convex surface and a conspicuous notch at the outer angle. 

 The rest separated from one another, rhomboidal, with a con- 

 spicuous notch at the outer angle, with strongly convex surface ; 

 more distally they become smaller, oval or round, and the surface 

 is so convex as to appear like hemispheric^ tul)ercles. The arm 

 spines are five in number in the proximal joints, but four in the 

 more distal ones. They are conical, blunt, solid, terete ; dorsal 

 ones longer and stouter ; in the basal joints of the arms, the 

 uppermost spine is about one and a half times, and the lowest 

 one about two-thirds, as long as the corresponding arm joint. 



Colour in alcohol yellowish brown. 



In younger specimens, the skin of the disk and arms is very 

 thick, and the buccal pores are often indistinct. 



This species is apparently near to 0. brachygnaiha, especially 

 in the disk coverings. But a careful comparison will show that, 

 the present species is more closely allied to 0. asaphcs than to 

 0. brachygnaiha, as shown in the foregoing key. 



Ophiosemnotes, g- nov. 



Disk high and convex, covered by a cereous skin, which 

 obscures the underlying stout scales ; beset with granules or stumpy 

 tubercles. Radial shields exposed, rounded or triangular, more or 

 less separated from each other. Three or four oral papillœ on 

 either side of each jaw. Teeth in a single vertical series. Dental 



