arONOGRAPH OF JAPANESE OPHIUROIDEA. 229 



pores very small. Dental papillœ about twenty-five in number, 

 forming a vertical, oval clump ; in the lower half they are very 

 small and arranged in four rows ; in the upper half they 

 are larger and arranged in two or three rows. Three teeth, 

 quadrangular, with truncated ends ; the lowest one is about as 

 long as the upper dental papillär ; the others are much longer 

 than the lowest, the uppermost one being the longest and narrowest. 

 Arms slender and short, vertically coiled, especially in the 

 distal parts. Dorsal arm plates large, quadrangular, with convex 

 outer border, about twice as wide as long, wider without than 

 within, very convex, so that the dorsal side of the arm is strong- 

 ly keeled as a whole. Four or five basal dorsal arm plates are 

 smaller and continued on to the radial row of disk scales. Some 

 of the dorsal arm plates are divided into equal or unequal halves. 

 Lateral arm plates not very prominent. First ventral arm plate 

 not very small, quadrangular, with curved inner and outer borders 

 and rounded angles, slightly wider than long, wider within than 

 without. Next one or two plates quadrangular, with curved outer 

 and concave lateral borders and rounded outer angles, slightly 

 longer than wide. Those beyond quadrangular, with concave inner 

 and outer Ijorders and rounded outer angles, wider than long. 

 The surface of the ventral arm plates are chagreened and covered 

 by a skin. The successive ventral arm plates are not in contact, 

 but are separated l)y a naked, depressed, groove-like space. Arm 

 spines six or seven in proximal free joints, conical, terete, tapered, 

 blunt ; the uppermost one is short, slightly longer than the corres- 

 ponding arm joint ; the next is the largest, longer than twice the 

 corresponding joint ; the others become shorter downwards, the 

 second lowest being slightly longer than the corresponding joint ; 

 the lowest spine is very small and short, serving as a tentacle 



